Liquid crystal display device, electronic device, and driving methods thereof

ABSTRACT

An object of the present invention is to provide a driving method by which excellent image quality and high video performance can be obtained as well as liquid crystal display devices and electronic devices with excellent image quality and high video performance. A pixel for monitor use is provided in a liquid crystal display device, and luminance of the pixel is detected using a light sensor. Herewith, because changes in luminance of a backlight with changes in the environment and the amount of time it takes for response of the liquid crystal become able to be calculated, control of the backlight in real time using the calculated information can be performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display devices,electronic devices, and driving methods for liquid crystal displaydevices and electronic devices.

2. Description of the Related Art

In recent years, replacement of display devices in which conventionalcathode-ray tubes are used with liquid crystal display devices as wellas employment of liquid crystal display devices in miniature electronicdevices has been progressing rapidly. Here, a liquid crystal displaydevice refers to a display device in which the alignment orientation ofliquid crystal molecules is changed by application of a voltage to theliquid crystal molecules which are interposed between substrates andchanges in optical characteristics produced thereby are used.

For a typical liquid crystal display device, for example, twistednematic (TN) liquid crystal display devices can be given. TN displayelements have as a basis a structure in-which a nematic liquid crystalis interposed between two substrates and the major axis of each of theliquid crystal molecules is twisted continuously along 90° between thetwo substrates. Consequently, the direction of polarization of lightincident on the liquid crystal molecules of the display elements in thisstate comes to be changed 90° along the twist of the liquid crystalmolecules.

Here, when a voltage is applied to the liquid crystal molecules, themajor axis of each of the liquid crystal molecules can be tilted in thedirection of the electric field by application of a voltage greater thanor equal to a certain threshold voltage V_(th). That is, the conditionof the twist of the liquid crystal molecules can be changed from 90°. Atthis time, the direction of polarization of light incident on the liquidcrystal molecules also comes to be changed according to this twist. A TNsystem is a system in which this principle is used as a light shutter.

By active matrix driving of the aforementioned TN system, a displaydevice with better video display performance than that with passivematrix driving can be realized. Here, active matrix driving refers todriving of a pixel by use of transistors that are built into each pixel.

By combination of a TN system and active matrix driving in this way, acertain level of performance for the display device is secured. However,if compared to a display device in which a conventional cathode-ray tubeis used, this display device is far from being in a state in which anacceptable level of performance (in particular, image quality and videoperformance) is obtained. In order to improve this performance,development of liquid crystal materials with fast response has beenprogressing (for an example of this, refer to Patent Document 1).Furthermore, systems such as OCB (bend orientation) systems and IPSsystems changing to TN systems are being employed more and more (for anexample of this, refer to Patent Document 2).

Moreover, an approach differing from that described above is also beingconsidered. For example, overdriving (for an example of this, refer toPatent Document 3) and impulse driving (for an example of this, refer toPatent Document 4) are each such an approach. Overdriving is a drivingmethod in which a high voltage is applied briefly in order to improvethe response speed of the liquid crystal molecules. The length of timeuntil the desired luminance is reached can be shortened, whereby thevideo performance is improved. In impulse driving, due to a backlightbeing turned off during a period (a transition period) in which targetgradation is not displayed, pulse-like (impulse-like) display isrealized so that video performance is improved and the amount ofvariation in gradation is reduced by the display being set to be blackdisplay during the transition period so that image quality is improved.

-   Patent Document 1: Japanese Published Patent Application No.    H5-17408-   Patent Document 2: Japanese Published Patent Application No.    H7-84254-   Patent Document 3: Japanese Published Patent Application No.    H7-104715-   Patent Document 3: Japanese Published Patent Application No.    2000-56738

SUMMARY OF THE INVENTION

In recent years, use of an LED as a backlight is being investigated. Ifan LED is used as a backlight, switching between the backlight beingturned on and the backlight being turned off at high speed becomespossible. Furthermore, use of an LED as a backlight has the advantagesof luminance characteristics at low temperature being about equal toluminance characteristics in a steady state, luminance being able to besecured instantaneously by input of source voltage, and high voltage notbeing needed.

However, even if an LED is used as a backlight, it does not necessarilymean that problems related to display will be solved completely. Forexample, the response speed of the liquid crystal changes significantlywith changes in the environment (for example, changes in temperature,air pressure, and the like). For this reason, when impulse driving isused, a mismatch between timing of the response of the liquid crystaland timing of when the backlight is turned on may occur. For example, incases in which control of the backlight being turned on and off isperformed at timing fixed by design, a state arises in which thebacklight is turned on even if response of the liquid crystal has notbeen completed. Consequently, display defects such as blurring of movingimages and the like come to be generated. Moreover, full advantagecannot be taken of the superior response characteristics of an LED.

In the same way, luminance of the backlight is also significantlyaffected by the environment. Consequently, it is difficult to say thatdesired luminance can be obtained no matter what the conditions are.

In view of the aforementioned problems, it is an object of the presentinvention to provide a driving method by which excellent image qualityand high video performance can be obtained as well as liquid crystaldisplay devices and electronic devices with excellent image quality andhigh video performance.

In the present invention, a pixel for monitor use is provided in aliquid crystal display device, and luminance of the pixel is detectedusing a light sensor. Herewith, because changes in luminance of abacklight with changes in the environment and the amount of time ittakes for response of the liquid crystal become able to be calculated,control of the backlight in real time using the calculated informationcan be performed. It is to be noted that the “real time” referred tohere does not mean “simultaneous” in the strict sense of the word butallows for slight differences in time that are imperceptible to humanbeings.

One aspect of a liquid crystal display device of the present inventionhas a backlight, a light source for monitor use, and a liquid crystallayer as well as a light sensor used to detect the intensity of lightpassing through the liquid crystal layer from the light source formonitor use. It is to be noted that the light source for monitor userefers to a light source which is used for monitoring the luminance.

Another aspect of a liquid crystal display device of the presentinvention is a liquid crystal display device that has a backlight, andthe liquid crystal display device also has a first polarizing plate overa light source for monitor use, a second polarizing plate over the firstpolarizing plate, a liquid crystal layer of a region wedged between thefirst polarizing plate and the second polarizing plate, and a lightsensor over the second polarizing plate where the light sensor isarranged so as to detect the intensity of light from the light sourcefor monitor use.

Furthermore, yet another aspect of a liquid crystal display device ofthe present invention is a liquid crystal display device that also has,in addition to what is given above, a unit for calculating an amount ofcorrection for luminance of the backlight based on the intensity oflight from the light source for monitor use that is detected by thelight sensor and a unit for controlling the luminance of the backlightbased on the amount of correction for the luminance of the backlightthat is calculated.

Moreover, another aspect of a liquid crystal display device of thepresent invention is a liquid crystal display device that also has, inaddition to what is given above, a unit for calculating timing of thebacklight being turned on and timing of the backlight being turned offbased on the luminance of light from the light source for monitor usethat is detected by the light sensor and a unit for controlling thebacklight being turned on and the backlight being turned off based onthe timing of the backlight being turned on and the timing of thebacklight being turned off that are calculated.

The light source for monitor use and the backlight described above mayeach be provided on one side of the liquid crystal layer. In addition,the light source for monitor use may be one part of the backlight.

Furthermore, for the light source for monitor use and the backlightdescribed above, the light source for monitor use may be provided on oneside of the liquid crystal layer and the backlight may be provided on aside of the liquid crystal layer opposite from the side on which thelight source for monitor use is provided.

Moreover, the liquid crystal display device that is described above mayalso have a light sensor that is used to detect the intensity ofexternal light. It is to be noted that a variety of electronic devicesin which the liquid crystal display device that is described above isused can be provided.

One aspect of a driving method for a liquid crystal display device ofthe present invention is a driving method of a liquid crystal displaydevice that has a backlight, a light source for monitor use, and aliquid crystal layer, and in the driving method for the liquid crystaldisplay device, the intensity of light passing through the liquidcrystal layer from the light source for monitor use is detected.

Furthermore, another aspect of a driving method for a liquid crystaldisplay device of the present invention is a driving method of a liquidcrystal display device in which, in addition to what is given above, anamount of correction for luminance of the backlight is calculated basedon the intensity of light from the light source for monitor use that isdetected by the light sensor, and the luminance of the backlight iscorrected based on the amount of correction for the luminance of thebacklight that is calculated.

Yet another aspect of a driving method for a liquid crystal displaydevice of the present invention is a driving method of a liquid crystaldisplay device in which, in addition to what is given above, timing ofthe backlight being turned on and timing of the backlight being turnedoff are calculated based on the intensity of light from the light sourcefor monitor use that is detected by the light sensor, and the backlightbeing turned on and the backlight being turned off is controlled basedon the timing of the backlight being turned on and the timing of thebacklight being turned off that are calculated.

The liquid crystal display device described above also has a lightsensor used to detect the intensity of light from external, and thedriving method for the liquid crystal display device may be one in whichan amount of correction for luminance of the backlight is calculatedbased on the brightness of surroundings detected by the light sensorthat is used to detect the intensity of light from external and theluminance of the backlight is controlled based on the amount ofcorrection for the luminance of the backlight that is calculated. It isto be noted that, in the present specification, “luminance” refers toinstantaneous brightness (instantaneous luminance) integrated over aconstant period of time.

By the present invention, because control corresponding to changes inthe environment (for example, temperature, air pressure, and the like)can be performed, display devices that have excellent image quality andhigh video performance can be provided. Furthermore, by the presentinvention, liquid crystal display devices and electronic devices inwhich excellent image quality and high video performance are exhibitedeven with major changes in the environment can be provided. That is,excellent image quality and high video performance can be obtained evenin display panels on streets that are subject to hostile environments,cellular phones, car electronics, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing an example of a structure of apanel of the present invention.

FIGS. 2A and 2B are diagrams showing examples of a circuit and a controlmethod of the present invention.

FIGS. 3A and 3B are diagrams showing examples of a circuit and a controlmethod of the present invention.

FIG. 4 is a diagram showing timing of when a backlight is turned on inthe present invention.

FIG. 5 is a diagram showing an example of a circuit of the presentinvention.

FIG. 6 is a diagram showing an example of a control method of thepresent invention.

FIG. 7 is a diagram showing timing of when a backlight is turned on inthe present invention.

FIG. 8 is a diagram showing an example of a control method of thepresent invention.

FIGS. 9A and 9B are diagrams showing examples of a structure of a panelof the present invention.

FIGS. 10A to 10D are diagrams showing examples of placement of a monitorsection in a liquid crystal display device of the present invention.

FIGS. 11A and 11B are diagrams showing examples of a structure of alight sensor of the present invention.

FIGS. 12A to 12D are diagrams illustrating a fabrication process of asemiconductor substrate of the present invention.

FIGS. 13A to 13C are diagrams illustrating a fabrication process of asemiconductor substrate of the present invention.

FIGS. 14A to 14C are diagrams illustrating a fabrication process of asemiconductor substrate of the present invention.

FIG. 15 is a diagram illustrating a fabrication process of a liquidcrystal display device of the present invention.

FIG. 16 is a diagram illustrating a top-view of a liquid crystal displaydevice of the present invention.

FIG. 17 is a diagram illustrating a cross-sectional-view of a liquidcrystal display device of the present invention.

FIGS. 18A and 18B are diagrams each illustrating a semiconductorsubstrate of the present invention.

FIGS. 19A and 19B are diagrams each illustrating cross-sectional viewsof a semiconductor substrate of the present invention.

FIGS. 20A and 20B are diagrams each illustrating cross-sectional viewsof a semiconductor substrate of the present invention.

FIGS. 21A to 21C are diagrams illustrating a fabrication process of asemiconductor substrate of the present invention.

FIGS. 22A to 22C are diagrams illustrating a fabrication process of asemiconductor substrate of the present invention.

FIGS. 23A to 23C are diagrams illustrating a fabrication process of asemiconductor substrate of the present invention.

FIGS. 24A and 24B are diagrams each illustrating a fabrication processof a semiconductor substrate of the present invention.

FIGS. 25A to 25C are diagrams illustrating a liquid crystal displaydevice of the present invention.

FIGS. 26A to 26D are diagrams illustrating a fabrication process of aliquid crystal display device of the present invention.

FIGS. 27A to 27C are diagrams illustrating a fabrication process of aliquid crystal display device of the present invention.

FIGS. 28A to 28C are diagrams illustrating a fabrication process of aliquid crystal display device of the present invention.

FIGS. 29A and 29B are diagrams each illustrating a different type ofdisplay device.

FIGS. 30A to 30H are diagrams illustrating electronic devices of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment Modes of the present invention will be described hereinafterwith reference to the accompanying drawings. However, the presentinvention is not limited to the description given hereinafter, and it isto be easily understood to those skilled in the art that various changesand modifications can be made without any departure from the spirit andscope of the present invention. Therefore, the present invention is notto be construed as being limited to the description of the embodimentmodes given hereinafter. It is to be noted that, in structures of thepresent invention described below, the same reference numerals are usedin common to denote the same components in different drawings.

Embodiment Mode 1

In the present embodiment mode, an example of a liquid crystal displaydevice and a driving method thereof of the present invention will bedescribed using FIGS. 1A and 1B and FIGS. 2A and 2B.

In FIG. 1A, a planar-view diagram of a panel in which the liquid crystaldisplay device of the present invention can be used is shown. Asubstrate 100 and a counter substrate 110 are bonded together by asealant 112. Furthermore, a pixel section 102, a scanning line drivercircuit 104 a, a scanning line driver circuit 104 b, and a monitorsection 108 are provided between the substrate 100 and the countersubstrate 110 and a signal line driver circuit 106 is provided over thesubstrate 100. Here, the monitor section 108 is a region in which alight sensor used to obtain luminance information of the panel isprovided. The area of the monitor section 108 may be approximately equalto the area of one pixel or may be larger than the area of one pixel. Bythe area of the monitor section 108 being increased, the level ofaccuracy in detection of luminance can be increased. Signals fromexternal are input via a flexible printed circuit (an FPC) 114. It is tobe noted that, in FIGS. 1A and 1B, the structure is one in which thescanning line driver circuit 104 a and the scanning line driver circuit104 b are formed integrally; however, the present invention is notlimited to having this structure. Furthermore, the placement of themonitor section is not limited to being that of the structure of FIG.1A. In addition, panel size can be selected and used as appropriate.

FIG. 1B is a diagram in which a simplified stacked-layer structure ofthe panel shown in FIG. 1A is shown. A liquid crystal layer 122 isprovided between a substrate 100 and a counter substrate 110.Furthermore, a polarizing plate 120 a and a polarizing plate 120 b areprovided on an outer side of the substrate 100 and an outer side of thecounter substrate 110 (the lower side of the substrate 100 and the upperside of the counter substrate 110 in the diagram), respectively. A lightsensor 124 is provided on an outer side of the polarizing plate 120 b(on the upper side of the polarizing plate 120 b).

The light sensor 124 detects light that passes through the polarizingplate 120 a, the substrate 100, the liquid crystal layer 122, thecounter substrate 110, and the polarizing plate 120 b in the ordergiven. Specifically, the light sensor 124 detects light from a backlight(or a light source for monitor use) that is provided on an outer side ofthe polarizing plate 120 a (the lower side of the polarizing plate 120 ain the diagram). Herewith, changes in the luminance of the backlightoccurring with changes in the environment (for example, changes intemperature, pressure, and the like) and the length of time for responseof the liquid crystal are calculated, whereby control of the backlight(for example, control of the luminance, control of the timing ofswitching, and the like of the backlight) can be performed. In thepresent embodiment mode, the structure was set to be one in which thelight sensor 124 was provided on an external part of the polarizingplate 120 a; however, the present invention is not limited to havingthis structure. Because an important point in implementation of thepresent invention is in detection of the intensity of light from abacklight (or a light source for monitor use) by the light sensor 124 incalculation of the amount of change in luminance and the length of timeneeded for response of the liquid crystal, if the light sensor 124 isplaced in a location at which the intensity of light from a backlight(or a light source for monitor use) can be detected, the presentinvention can be implemented in the same way without being limited tohaving the structure of the present embodiment mode. Of course, thestructure may be set to be one in which a plurality of light sensors areprovided, and the arrangement thereof can be set as appropriate. It isto be noted that in order that accurate control of the present inventionbe performed, it is important that the structure be set to be one inwhich the light incident on the light sensor 124 is not any light otherthan the light that is the object of detection.

It is to be noted that, although the light incident on the light sensormay be light from the backlight, it is even more preferable that a lightsource for monitor use be provided in addition to the backlight. Casesin which light from a backlight is used are preferable because thestructure can be simplified in such cases. In cases in which a lightsource for monitor use is provided in addition to the backlight,different control methods in which the light source for monitor use isused can be combined together as appropriate. For the light source formonitor use, it is preferable that a light source that has the samecharacteristics as those of the backlight be used; however, if theluminance of the light source for monitor use and the luminance of thebacklight are to have a correspondence relationship, then the presentinvention is not to be taken as being limited to use of a light sourcewith the same characteristics as those of the backlight. In the presentembodiment mode, cases in which a light source is provided in additionto a backlight are to be described.

It is to be noted that, in FIG. 1B, a structure in which light isextracted from a counter substrate side is shown; however, the presentinvention can be used in a structure in which light is extracted from asubstrate (active matrix substrate) side in the same way. In this case,the light sensor is to detect light that passes through a polarizingplate, a counter substrate, a liquid crystal layer, a substrate (anactive matrix substrate), and a polarizing plate in the order given.

Next, an example of a circuit that controls output (luminance) of abacklight of a liquid crystal display device of the present inventionand an example of a control method for control of the output (luminance)of the backlight will be described using FIGS. 2A and 2B. It is to benoted that control of output of the backlight in the present embodimentmode is performed in order that the intended, proper brightness bedisplayed for cases right after power is turned on, cases in which theenvironment changes, and the like when the brightness of the backlightis not the intended brightness.

FIG. 2A is a diagram illustrating an example of a circuit that controlsthe output (luminance) of the backlight. A light sensor 200 iselectrically connected to an integrator circuit 202, and the integratorcircuit 202 is electrically connected to a comparator circuit 204. Thecomparator circuit 204 is electrically connected to a backlight controlcircuit 206, and the backlight control circuit 206 is electricallyconnected to a backlight 208 and a light source 210 for monitor use.Light from the light source 210 for monitor use passes through a liquidcrystal panel 212 to be incident on the light sensor 200. It is to benoted that, in FIG. 2A, the connection relationship between thebacklight control circuit 206 and the backlight 208 and light source 210for monitor use is shown; however, for cases in which the light sourcefor monitor use is used in common with the backlight so that the lightsource for monitor use is omitted, the structure may be set to be one inwhich the backlight control circuit 206 is electrically connected to thebacklight 208 only. Arrows in the diagram indicate the direction oftransmission of principal signals.

The integrator circuit 202 has a role of time integration of lightintensity (instantaneous luminance) detected by the light sensor. Humanbeings have a trait by which light intensity over a given period of timeis integrated and perceived. For this reason, by use of the integratorcircuit 202, the amount of luminance that is received by a human eye canbe calculated.

The comparator circuit 204 has a role of comparison of the amount ofluminance obtained by the integrator circuit 202 with a value determinedin advance. The backlight control circuit 206 controls the backlight 208and the light source 210 for monitor use based on the results of thecomparison made by the comparator circuit 204.

Here, using FIG. 2B, an example of a control method of output(luminance) of a backlight will be described. At first, target luminanceA is specified (Step S250). In the present embodiment mode, for anexample, a case in which the output of the backlight can be adjusted 256levels “from 0 to 255” and in which the mode can be switched between anyof a plurality of modes (for example, sunlight mode, interior lightmode, darkroom mode, and the like) depending on the brightness of thesurroundings will be considered. For example, the output of thebacklight in sunlight mode is set to be 200, the output of the backlightin interior light mode is set to be 150, and the output of the backlightin darkroom mode is set to be 100. If the display mode being employed issunlight mode, intended original brightness for output of 200, voltageapplied to a pixel electrode of the monitor section, and the like areused as a reference by which the target luminance A can be set. Morespecifically, for example, the brightness of the backlight is set to bethe original brightness in cases in which the output is 200, wherebyluminance for cases in which a voltage by which luminance is maximizedis applied to the pixel electrode of the monitor section can be set tobe the target luminance A. It is to be noted that, because the presentembodiment mode is related to control of output of the backlight, thereare no particular limitations on the voltage applied to the pixelelectrode of the monitor section; however, in order that control of theoutput of the backlight be performed with a high level of accuracy,having a greater amount of light be incident on the light sensor ispreferable. It is to be noted that the structure may be set to be one inwhich information about the target luminance A is stored in memory inadvance and read out from the memory and used as appropriate.

Next, luminance B of a monitor section during one frame period isdetected (Step S252). It is to be noted that the luminance detection forcontrol of the output of the backlight is to be referred to as“luminance detection for output control” for descriptive purposes.

Then, the target luminance A and the aforementioned luminance B arecompared, and a request is made for parameters used for correction (StepS254). Here, for a calculation method of the parameters used forcorrection, a method in which the difference between the targetluminance A and the detected luminance B is used, a method in which theratio of the target luminance A to the detected luminance B is used, andthe like can be given. For example, the calculation method ofcalculation by ratio can be used in cases in which the output(luminance) of the backlight changes linearly with respect to input. Inthis case, because the relationship between an input current I₁ used toobtain the target luminance and an input current I₂ of actual conditionsis represented as A:B=I₁:I₂, the amount of the input current I₁ neededto obtain the target luminance is I₁=I₂·(A/B). In the present embodimentmode, because the output of the backlight can be controlled at 256steps, in adjustment of the luminance of the backlight, a step duringwhich an amount of electric current the value of which is fairly closeto the value of the electric current described above comes to beselected. It is to be noted that, in cases in which the luminance of thebacklight is to change linearly with respect to input voltage, theoutput of the backlight can be controlled in the same way using voltage.

In cases in which the output (luminance) of the backlight does notrespond linearly with respect to the input parameters, use of the methodin which the amount of difference is used is preferable. That is, arequest is made for a difference C(=A−B) between the target luminance Aand the detected luminance B, and the electric current, voltage, and thelike input to the backlight are specified using a reference table (aso-called lookup table).

Next, the luminance of the backlight is adjusted using the parametersthat are used for correction calculated using any of the aforementionedmethods or the like (Step S256). It is to be noted that, even in casesin which control is performed using the difference C, the electriccurrent, voltage, and the like input to the backlight are not limited tobeing specified with reference to a lookup table. For example, a methodin which the amount of the input current (or input voltage) input to thebacklight is changed for each given step can be employed. In this case,if the amount of electric current (or voltage) for maximum luminance isset to be represented by I_(MAX) (or V_(MAX)), then the amount of inputcurrent (or input voltage) is changed by I_(MAX)/N (or V_(MAX)/N), whichis one step, for cases in which luminance control is performed in Nsteps. By the structure being set to be like this structure, althoughthe length of time needed for reaching target luminance is increasedsomewhat, there is an advantage with this method in that lookup tablesneed not be provided. Furthermore, for cases in which a light source formonitor use is provided in addition to a backlight, as in the presentembodiment mode, for feedback performed during a subsequent step, thereis a need for adjustment of the luminance of the light source formonitor use to be performed at the same time.

Next, the target luminance A and a luminance B′ after correction arecompared (Step S258). In cases in which the target luminance A and theluminance B′ after correction come to be equal (cases in which A=B′),correction is finished for the time being. In cases in which the targetluminance A and the luminance B′ after correction do not come to beequal due to changes in the environment and a margin of error and thelike in the correction, once again, a request is made for the parametersfor correction use, and correction is performed (Step S252 and StepS254). By repetition of this kind of feedback, eventually, the targetluminance A comes to be displayed. It is to be noted that, in thepresent embodiment mode, the structure is set to be one in whichfeedback is repeated until the target luminance A and the luminance B′after correction come to be equal to each other; however, the presentinvention is not to be taken as being limited to this structure only.For example, in cases in which a certain amount of margin with respectto the target luminance A is provided and the luminance B′ aftercorrection falls within that range, the structure can be set to be onein which correction is then finished.

It is to be noted that in the flow shown in FIG. 2B, when correction iscompleted, correction is finished; however, the present invention is notlimited to this configuration. For example, the structure may be set tobe one in which correction is performed for each constant period, or thestructure may be set to be one in which feedback is constantly given. Inaddition, the structure can be set to be one in which correction isperformed whenever the display mode is switched from one display mode toanother (for example, when the display mode is switched from sunlightmode to interior light mode). Furthermore, the present invention can beapplied both to cases in which the detected luminance B is lower thanthe target luminance A and to cases in which the detected luminance B ishigher than the target luminance A. Of course, the state of the presentinvention may also be one in which the detected luminance B is equal tothe target luminance A.

As described above, by performance of control of the output (luminance)of a backlight using a light sensor, desired luminance can be displayedcorrectly. Furthermore, even in cases in which the output of thebacklight changes with changes in the environment (temperature,pressure, and the like), desired luminance can be maintained. Inaddition, because temperature sensors and the like used to detectchanges in the environment become unnecessary and there is no need touse a lookup table for reference of the relationship between temperatureand the like and luminance, structures of sensors, memory, and the likecan be simplified.

In addition, even in states in which no time passes from input ofelectricity and in states in which a constant period of time passes frominput of electricity, excellent image quality that does not change canbe provided. Furthermore, excellent image quality can be obtained evenin display panels on streets that are subjected to hostile environments,cellular phones, car electronics, and the like.

It is to be noted that, in the present embodiment mode, an example isgiven in which processing is performed using hardware; however, thepresent invention is not to be taken as being limited to thisconfiguration. Because a technical idea of the present embodiment modeis that control of output (optimization of output) of a backlight isperformed based on information obtained from a light sensor, any type ofstructure can be employed as long as it is a structure in which thistechnical idea can be implemented. For example, processing performedusing hardware in the present embodiment mode can also be performedusing software.

It is to be noted that in the present embodiment mode, cases in whichthe present invention is applied to a liquid crystal display device aredescribed; however, the present invention can be used in display devicesother than liquid crystal display devices. For example, the presentinvention can be used for compensation of a drop in luminance thatoccurs with deterioration of light-emitting elements in anelectroluminescent display device in which the light-emitting elementsare used. In particular, if the structure is set to be one in whichcompensation is made for luminance in each RGB, provision of extremelyhigh-level image quality becomes possible. In the same way, the presentinvention can be used in a display device such as a plasma display panel(a PDP), a field emission display (an FED), and the like, as well.

Embodiment Mode 2

In the present embodiment mode, another example of a liquid crystaldisplay device and a driving method thereof of the present inventionwill be described using FIGS. 3A and 3B and FIG. 4.

Because the structure of a panel that can be used in a liquid crystaldisplay device of the present embodiment mode is the same as that ofEmbodiment Mode 1, a detailed description thereof will be omitted. Inthe present embodiment mode, an example of a switching control circuitthat controls switching of a backlight and an example of switchingcontrol method for control of switching of a backlight will bedescribed. It is to be noted that control of switching of a backlight isperformed so that timing of on and off of the backlight is controlled sothat correct grayscale is displayed in cases in which correct grayscaleis not displayed due to lag in the response of the liquid crystal,timing of writing, and the like.

FIG. 3A is a diagram illustrating an example of a switching controlcircuit that controls switching of the backlight. A light sensor 300 iselectrically connected to an integrator circuit 302, and the integratorcircuit 302 is electrically connected to a comparator circuit 304. Thecomparator circuit 304 is electrically connected to a backlight controlcircuit 306, and the backlight control circuit 306 is electricallyconnected to a backlight 308 and a light source 310 for monitor use.Light from the light source 310 for monitor use passes through a liquidcrystal panel 312 to be incident on the light sensor 300. It is to benoted that, in FIG. 3A, the connection relationship between thebacklight control circuit 306 and the backlight 308 and light source 310for monitor use is shown; however, for cases in which the light sourcefor monitor use is used in common with the backlight so that the lightsource for monitor use is omitted, the structure may be set to be one inwhich the backlight control circuit 306 is electrically connected to thebacklight 308 only. Arrows in the diagram indicate the direction oftransmission of principal signals.

The integrator circuit 302 has a role of time integration of lightintensity (instantaneous luminance) detected by the light sensor. Humanbeings have a trait by which light intensity over a given period of timeis integrated and perceived. For this reason, by use of the integratorcircuit 302, the amount of luminance that is received by a human eye canbe calculated.

It is to be noted that, in the present embodiment mode, a structure isshown in which the integrator circuit 302 is provided; however, thepresent invention is not limited to having this structure only. Becausecontrol in the present embodiment mode is control performed usinginstantaneous luminance, the structure may be set to be one in which theintegrator circuit 302 need not be provided. By provision of theintegrator circuit 302, more accurate control can be performed byreduction of the effects of noise. With cases in which the integratorcircuit 302 is not provided, there is an advantage in that the structurecan be simplified even more.

The comparator circuit 304 has a role of comparison of the amount ofluminance obtained by the integrator circuit 302 with a value determinedin advance. The backlight control circuit 306 controls the backlight 308and the light source 310 for monitor use based on the results of thecomparison made by the comparator circuit 304. It is to be noted that,in the present embodiment mode, the structure may be set to be one inwhich the light source 310 for monitor use is constantly turned on, orthe structure may be set to be one in which the light source 310 formonitor use is turned off during periods in which the light source 310for monitor use is not needed. For example, the structure can also beset to be one in which the light source 310 for monitor use is turnedoff during subsequent frame periods in cases in which timing of thebacklight 308 being turned off is fixed. Herewith, compared to cases inwhich the light source 310 for monitor use is made to emit lightconstantly, power consumption can be reduced.

Here, using FIG. 3B, an example of a switching control method forcontrol of switching of the backlight will be described. At first, atarget luminance D is specified (Step S350). It is preferable that thetarget luminance D be specified assuming a state in which the responsespeed is slowest, that is, a state in which the greatest amount of timeis needed for completion of response, in this liquid crystal displaydevice. For example, because the response to intermediate grayscale isslowest in a VA liquid crystal display device, the luminance for theaforementioned intermediate grayscale may be set to be the targetluminance D. Herewith, the maximum amount of time needed for thisresponse to be completed from input of a signal to one pixel isobtained. That is, timing of the backlight being turned on can be madeto match the state in which the response becomes slowest. Hence, thebacklight can be made to turn on after the response of all pixels thatform one screen is completed, which leads to an improvement in videoperformance. It is to be noted that, in order that this kind of displaybe realized, for example, after a signal is input to the last pixel ofthe screen, the backlight may be turned on according to the requestedtiming for the backlight being turned on.

Next, a threshold value E is specified (Step S352). The threshold valueE is a value that becomes a reference for switching of the backlight.Specifically, the threshold value E is a reference value used todetermine if the target luminance has been reached or not; for example,in cases in which the response of the luminance is determined to havegone from a state of low luminance to a state of high luminance, thetarget luminance is considered as having been reached if the luminanceis greater than or equal to the threshold value E. The threshold value Ecan be specified as appropriate so as to match targets for imagecharacteristics and video performance. In addition, the threshold valueE may be set using the target luminance D as a reference. In the presentembodiment mode, for an example is given a case in which the response ofthe luminance is determined to have gone from a state of low luminanceto a state of high luminance, and a case in which the threshold value Eis set to be 95% of the target luminance D will be described. It is tobe noted that, in cases in which the response of the luminance isdetermined to have gone from a state of high luminance to a state of lowluminance, the target luminance may be considered as having been reachedif the luminance is less than or equal to the threshold value E.

It is to be noted that in the case of use in an application in whichonly still images are displayed, control of switching of the backlightshown in the present embodiment mode may be set so as not to beperformed, in practice. Herewith, because “instantaneous luminance” ofthe backlight in cases in which display is performed at a constantluminance can be kept low, there is an advantage with this case in thatthe length of the life of the backlight is improved.

Next, one frame period is divided up into an F number of periods(hereinafter referred to as luminance detection periods) of equal length(Step S354). It is to be noted that, in the present embodiment mode, foran example, a case in which one frame period is divided up into 30luminance detection periods will be described. Here, for cases in whichthe response of the liquid crystal is not completed during one frameperiod, there is no need for one frame period to be set to be a testperiod during which control of switching of the backlight is performed.For example, in some liquid crystal display devices and the like inwhich a liquid crystal material with a slow response is used, there arecases in which the response of the liquid crystal is not completedduring one frame period. In these kinds of cases, control can beperformed with two or more frame periods being set to be test periods.Meanwhile, when the response speed of liquid crystal display devices ofrecent years is considered, in many liquid crystal display devices, theresponse of the liquid crystal is generally completed within one frameperiod. Consequently, in the present embodiment mode, an example will bedescribed in which control of switching of the backlight is performedwith one frame period being set to be a test period. Of course, thepresent invention can be implemented even in cases in which the drivingfrequency is increased (double speed (120 Hz) driving, triple speed (180Hz) driving, and the like). For example, in cases in which one frameperiod is divided up into an n number of subframe periods and n-speeddriving is performed, the structure may be set to be one in whichwriting of a signal to all pixels is made to be completed during a firstsubframe period, and the length of time needed for response of theliquid crystal is calculated using one or a plurality of subframeperiods including the first subframe period.

It is to be noted that, as in the present embodiment mode, during aperiod different from a frame period that is a reference, in order thatsome kind of operation (in the present embodiment mode, this operationcorresponds to that of the above-described “detection of luminanceduring a luminance detection period”), a new timing signal correspondingto the target timing becomes needed. Here, for generation of a newtiming signal in a simple structure, a clock signal input to a drivercircuit may be used. For example, by performance of logic operations(for example, AND operations) performed based on outputs of an(N-1)^(th) shift register and an N^(th) shift register in the drivercircuit, a new timing signal can be generated in an extremely simplestructure. Furthermore, by the number of the stage of a selected shiftregister being changed as appropriate, a great variety of timing signalscan be generated in a fairly simple structure. Alternatively, timingsignals may be generated by frequency divider circuits and the likebeing combined together as appropriate.

Next, a luminance G in one luminance detection period is detected (StepS356). Here, the luminance detection for control of switching of thebacklight is to be referred to as “luminance detection for switchingcontrol” for descriptive purposes. Next, the luminance G detected duringthe luminance detection period is compared to the threshold value E perluminance detection period, E/F (Step S358). When the detected luminanceG exceeds the threshold value E per luminance detection period, E/F (oris greater than or equal to E/F), the backlight is turned on at thattiming (Step S360); when such is not the case, a luminance G′ isdetected during the next luminance detection period, and the same typeof comparison is made (Step S356, Step S358). Here, the structure may beset to be one in which the backlight is turned off for states in whichthe detected luminance is less than the threshold value. It is to benoted that E/F is used as the object of comparison because E is athreshold value that is set based on the target luminance D and E/F isrepresented as the integral value of one frame period. Meanwhile, anintegration period in detection of the luminance G is 1/F of one frameperiod.

It is to be noted that, in the present embodiment mode, operations ofpixels in a monitor section may be performed separately from operationsof pixels in a display section, or the operations of pixels in thedisplay section may be performed simultaneous with the operations ofpixels in a monitor section. In cases in which the operations of pixelsin the monitor section are performed simultaneous with the operations ofpixels in the display section, it is preferable that operations be madeto be performed simultaneously with respect to the last pixel in thedisplay section to which a signal is written. By operations being madeto be performed simultaneously with respect to the last pixel in thedisplay section to which a signal is written, the timing at which theresponse of the liquid crystal in all pixels on the screen is completedbecomes easy to calculate. In cases in which the operations of thepixels in the monitor section are performed separately from theoperations of the pixels in the display section, the timing for thebacklight being switched on and off may be corrected as appropriate.

As described above, timing for the backlight being switched on and offcan be set according to the flow shown in FIG. 3B. The set timing isstored in memory and can be used for a given continuous period of time.Of course, the structure may also be set to be one in which the timingof the backlight being switched on and off is changed for each frameperiod.

FIG. 4 is a graph showing a relationship between luminance(instantaneous luminance) and timing for the backlight being turned onfor cases in which the switching timing control method for control ofthe timing of the backlight being switched on and off shown in thepresent embodiment mode is used. The vertical axis in the graphrepresents luminance when the target luminance is set to be 100. Thehorizontal axis represents luminance detection periods for one frameperiod (from a first luminance detection period to a thirtieth luminancedetection period). Furthermore, luminance greater than or equal to thethreshold value is represented in a region 400, and a period duringwhich the backlight is turned on is represented in a region 402. Arrowsin the graph indicate that it has been determined that the luminance hasexceeded the threshold value for periods from the arrows onward (forperiods from a sixteenth luminance detection period). In the presentembodiment mode, a case is described in which the threshold value of theluminance is set to be 95% of the target luminance and one frame periodis divided up into 30 luminance detection periods; however, the presentinvention is not to be taken as being limited to this configuration.Various parameters can be changed as appropriate.

In the case of FIG. 4, the luminance does not exceed the threshold valueuntil after the fifteenth luminance detection period. For this reason,from the seventeenth luminance detection period, which is the luminancedetection period subsequent to the sixteenth luminance detection periodduring which the threshold value is exceeded, the backlight is turnedon. It is to be noted that the luminance represented by the curved linein FIG. 4 is “instantaneous luminance” and does not strictly correspondto the “luminance” found by time integration. In addition, in thepresent embodiment mode, there is time lag between the timing at whichluminance greater than or equal to the threshold value is detected andthe timing at which the backlight is turned on. For example, as shown inFIG. 4, even though the luminance detection period during which thethreshold value is exceeded is the sixteenth luminance detection period,the backlight being turned on starts from the seventeenth luminancedetection period. This is because the luminance is determined by timeintegration during one luminance detection period. However, this problemcan be solved by the length of a luminance detection period, which is anintegration period, being shortened enough (that is, by one frame periodbeing divided up into a number of luminance detection periods).

Moreover, to solve this kind of problem, the structure is set to be onein which luminance determined by time integration is not used, butrather, determination is performed using instantaneous luminance. Theuse of instantaneous luminance has the same meaning as the length of theintegration period being shortened enough (that is, the same meaning asone frame period being divided up into an almost infinite number ofluminance detection periods). By the structure being set to be this kindof structure, timing of the backlight being turned on can be controlledeven more finely. In cases in which luminance determined by timeintegration is used, even if the length of a luminance detection period,which is an integration period, cannot be shortened enough, for example,when the timing of control of the backlight is retained in memory andconstant control is performed for a given period at the same timing, acorrection is added as appropriate (in the case of FIG. 4, the timingfor the backlight being turned on is switched from being during theseventeenth luminance detection period to being during the sixteenthluminance detection period), and the timing for the backlight beingturned on can be optimized even more.

It is to be noted that when the display device becomes able to operateat high speed, problems caused by noise or the like may arise. Forexample, in cases such as that shown in FIG. 4 where the effects ofnoise are small and luminance increases (or decreases) by one step,there are no problems, in particular; however, when there is a largeamount of noise, a state may occur in which the threshold value isexceeded temporarily. In this kind of state, accurate control of thebacklight is difficult. To solve this problem, for example, a newcondition, which is that “the backlight is to be turned on when thedetected luminance exceeds the threshold value at least two times (ormore than two times) in a row,” may be added. Because the same kind ofproblem may occur when overdriving is used, it is preferable that thesame kind of measures be performed in that case, as well.

It is to be noted that, in the present embodiment mode, a case in whichthe case of the luminance being changed from a state of low luminance toa state of high luminance is set to be a test pattern is described;however, the present invention is not to be taken as being limited tothis case only. The present invention can also be used in a structure inwhich the case of the luminance being changed from a state of highluminance to a state of low luminance is set to be a test pattern. Inthis case, different parameters may be changed as appropriate.

As described above, by performance of control of the switching of thebacklight using a light sensor, the realization of impulse driving byoptimal timing becomes possible. Herewith, video performance is improveddramatically. Furthermore, even in cases in which the response speed ofthe liquid crystal changes with changes in the environment (temperature,pressure, and the like), because optimal impulse driving can berealized, the video performance can be maintained at a high levelconstantly. In addition, because temperature sensors and the like usedto detect changes in the environment become unnecessary and there is noneed to use a reference table (a so-called lookup table) for control ofthe switching of the backlight, structures of sensors, memory, and thelike can be simplified.

It is to be noted that impulse driving for cases in which the presentinvention is used is different from impulse driving in the conventionalmeaning. That is, while conventional impulse driving refers to luminanceof one pixel changing in a pulse-like manner, impulse driving realizedby use of the present invention refers to luminance of pixels of onescreen changing simultaneously and in a pulse-like manner. To furtherreiterate, while conventional impulse driving is impulse driving bypoint-sequential driving or line-sequential driving, impulse drivingrealized by use of the present invention has a kind of aspect of pixelsfor one screen being turned on simultaneously, a “frame-sequentialdriving” kind of aspect. Because all pixels for one screen can be turnedon simultaneously, video performance can be dramatically improved. It isto be noted that, to realize the above-described impulse driving, thelength of an intended period (one frame period in the present embodimentmode) needs to be longer than the sum of the length of time needed forwriting of a signal to all pixels and the length of time needed forcompletion of the response of the liquid crystal of all pixels. This isattributed to the fact that turning on of the backlight starts from astate in which the response of the liquid crystal of all pixels iscompleted. However, in view of improvements in processing capability ofdriver circuits, improvements in the response speed of a liquid crystal,and the like in recent years, this point does not cause any problems inparticular.

In addition, even in states in which no time passes from input ofelectricity and in states in which a constant period of time passes frominput of electricity, a liquid crystal display device exhibiting highvideo performance can be provided. Furthermore, high video performancecan be obtained even in display panels on streets that are subject tohostile environments, cellular phones, car electronics, and the like.

It is to be noted that, in the present embodiment mode, a description isgiven for cases in which control of switching of a backlight isperformed; however, the present invention can be used in cases otherthan in cases in which control of switching of a backlight is performed.For example, the present invention can also be used to determine optimalvoltage in overdriving. In this case, by overdrive voltage beingcontrolled so that display is performed at a given luminance by adesired period, video performance can be improved dramatically. Ofcourse, control of overdrive voltage and control of switching of thebacklight may be used in combination with each other.

Furthermore, in the present embodiment mode, an example is given inwhich processing is performed using hardware; however, the presentinvention is not to be taken as being limited to this configuration.Because a technical idea of the present embodiment mode is that controlof switching of a backlight is performed based on information obtainedfrom a light sensor, any type of structure can be employed as long as itis a structure in which this technical idea can be implemented. Forexample, processing performed using hardware in the present embodimentmode can also be performed using software.

The present embodiment mode can be used in combination with EmbodimentMode 1, as appropriate. It is to be noted that the output control of theoutput of a backlight shown in Embodiment Mode 1 and control ofswitching of a backlight in the present embodiment mode can be used incombination with each other. By the structures being used in combinationwith each other, a liquid crystal display device with excellent imagequality and high video performance is realized.

Embodiment Mode 3

In the present embodiment mode, another example of a liquid crystaldisplay device and a driving method thereof of the present inventionwill be described using FIG. 5, FIG. 6, and FIG. 7.

Because the structure of a panel that can be used in a liquid crystaldisplay device of the present embodiment mode is the same as that ofEmbodiment Mode 1, a detailed description thereof will be omitted. Inthe present embodiment mode, an example of a switching control circuitthat controls switching of a backlight and an example of switchingcontrol method for control of switching of a backlight different fromthose of Embodiment Mode 2 will be described.

FIG. 5 is a diagram illustrating an example of a switching controlcircuit that controls switching of the backlight. A light sensor 500 iselectrically connected to an integrator circuit 502, and the integratorcircuit 502 is electrically connected to a comparator circuit A 504, adifferential circuit 506, and a delay circuit 508. The delay circuit 508is electrically connected to the differential circuit 506, and thedifferential circuit 506 is electrically connected to a comparatorcircuit B 510. The comparator circuit A 504 and the comparator circuit B510 are electrically connected to a coincidence circuit 512, thecoincidence circuit 512 is electrically connected to a backlight controlcircuit 514, and the backlight control circuit 514 is electricallyconnected to a backlight 516 and a light source 518 for monitor use.Light from the light source 518 for monitor use passes through a liquidcrystal panel 520 to be incident on the light sensor 500. It is to benoted that, in FIG. 5, the connection relationship between the backlightcontrol circuit 514 and the backlight 516 and the light source 518 formonitor use is shown; however, for cases in which the light source formonitor use is used in common with the backlight so that the lightsource for monitor use is omitted, the structure may be set to be one inwhich the backlight control circuit 514 is electrically connected to thebacklight 516 only. Arrows in the diagram indicate the direction oftransmission of principal signals.

The integrator circuit 502 has a role of time integration of lightintensity (instantaneous luminance) detected by the light sensor. Humanbeings have a trait by which light intensity over a given period of timeis integrated and perceived. For this reason, by use of the integratorcircuit 502, the amount of luminance that is received by a human eye canbe calculated.

It is to be noted that, in the present embodiment mode, a structure isshown in which the integrator circuit 502 is provided; however, thepresent invention is not limited to having this structure only. Becausecontrol in the present embodiment mode is control performed usinginstantaneous luminance, the structure may be set to be one in which theintegrator circuit 502 need not be provided. By provision of theintegrator circuit 502, more accurate control can be performed byreduction of the effects of noise. With cases in which the integratorcircuit 502 is not provided, there is an advantage in that the structurecan be simplified even more.

The comparator circuit A 504 has a role of comparison of the amount ofluminance obtained by the integrator circuit 502 with a value determinedin advance. The differential circuit 506 calculates the amount ofdifference between luminance obtained by the integrator circuit 502 andluminance during the previous luminance detection period obtained by thedelay circuit 508. The comparator circuit B 510 has a role of comparisonof the amount of difference obtained by the differential circuit 506with a value determined in advance. The coincidence circuit 512determines whether the comparison results of the comparator circuit A504 and the comparison results of the comparator circuit B 510 bothfulfill the conditions or not. The backlight control circuit 514controls the backlight 516 and the light source 518 for monitor usebased on signals from the coincidence circuit 512. It is to be notedthat, in the present embodiment mode, it is preferable that thestructure be set to be one in which the light source 518 for monitor useis constantly turned on; however, the present invention is not to betaken as being limited to this kind of structure only.

Here, using FIG. 6, an example of a switching control method for controlof switching of the backlight will be described. At first, a targetluminance H is specified (Step S600). It is preferable that the targetluminance H be specified assuming a state in which the response speed isslowest, that is, a state in which the greatest amount of time is neededfor completion of response, in this liquid crystal display device. Forexample, because the response to intermediate grayscale is slowest in aVA liquid crystal display device, the luminance for the aforementionedintermediate grayscale may be set to be the target luminance H. By thetarget luminance H being set in consideration of the state in which theresponse becomes slowest, the backlight can be made to turn on after theresponse of all pixels that form one screen is completed. This leads toan improvement in video performance.

Next, a threshold value I and a threshold value J are specified (StepS602). The threshold value I and the threshold value J are values thatare used as a reference for switching of the backlight. Specifically,the threshold value I is a reference value used to determine if thetarget luminance has been reached or not; for example, in cases in whichthe response of the luminance is determined to have gone from a state oflow luminance to a state of high luminance, the target luminance isconsidered as having been reached if the luminance is greater than orequal to the threshold value I. The threshold value J is a referencevalue used to determine if the luminance is stable or not; if the amountof change in the luminance is less than or equal to the threshold valueJ, the luminance is considered to be stable. The threshold value I andthe threshold value J can be specified as appropriate so as to matchtargets for image characteristics and video performance. In addition,the threshold value I and the threshold value J may be set using thetarget luminance H as a reference. In the present embodiment mode, foran example is given a case in which the response of the luminance isdetermined to have gone from a state of low luminance to a state of highluminance, and a case in which the threshold value I is set to be 95% ofthe target luminance H will be described.

It is to be noted that in the case of use in an application in whichonly still images are displayed, control of switching of the backlightshown in the present embodiment mode may be set so as not to beperformed, in practice. By the configuration being set in this way,because “instantaneous luminance” of the backlight in cases in which thesame luminance is displayed can be kept low, there is an advantage withthis case in that the length of the life of the backlight is improved.

It is to be noted that in cases in which the backlight is controlled foreach display region, the structure may be set to be one in which athreshold value is set for each display region. That is, by control ofswitching of the backlight shown in the present embodiment mode beingset so as not to be performed in practice in regions in which only stillimages are displayed, in regions in which moving images are displayed,the threshold value I may be set as appropriate according to requestedimage performance. By the configuration being set in this way,optimization of the screen in cases with still image regions and movingimage regions comes to be possible.

It is preferable that the threshold value J be specified inconsideration of the amount of noise and the like. For example, if theaverage noise level is about 1% of the target luminance H, then thethreshold value J needs to be set so as to be greater than or equal to1% of the target luminance H. However, because the threshold value Jbecomes unable to be used to determine whether the luminance is stableor not if increased too much, the threshold value J may be set to be ofan approximate value by which the luminance can be determined to bestable or not while the noise level is being considered. As an examplein the present embodiment mode, a case in which the threshold value J isset to be 1% of the target luminance H will be described.

Next, one frame period is divided up into a K number of periods(hereinafter referred to as luminance detection periods) of equal length(Step S604). It is to be noted that, in the present embodiment mode, foran example, a case in which one frame period is divided up into 30luminance detection periods will be described. Here, for cases in whichthe response of the liquid crystal is not completed during one frameperiod, there is no need for one frame period to be set to be a testperiod during which control of switching of the backlight is performed.For example, in a liquid crystal display device and the like in which aliquid crystal material with a slow response is used in one part of theliquid crystal display device, there are cases in which the response ofthe liquid crystal is not completed during one frame period. In thesekinds of cases, control can be performed with two or more frame periodsbeing set to be test periods. Meanwhile, when the response speed ofliquid crystal display devices of recent years is considered, in manyliquid crystal display devices, the response of the liquid crystal isgenerally completed within one frame period. Consequently, in thepresent embodiment mode, an example will be described in which controlis performed with one frame period being set to be a test period. Ofcourse, the present invention can be implemented even in cases in whichthe driving frequency is increased (for example, double speed (120 Hz)driving, triple speed (180 Hz) driving, and the like). For example, incases in which one frame period is divided up into an n number ofsubframe periods and n-speed driving is performed, the structure may beset to be one in which writing of a signal to all pixels is made to becompleted during a first subframe period, and the length of time neededfor response of the liquid crystal is calculated using one or aplurality of subframe periods including the first subframe period.

It is to be noted that, as in the present embodiment mode, during aperiod different from a frame period that is a reference, in order thatsome kind of operation (in the present embodiment mode, this operationis related to the above-described “detection of luminance during aluminance detection period”), a new timing signal corresponding to thetarget timing becomes needed. Here, for generation of a new timingsignal in a simple structure, a clock signal input to a driver circuitmay be used. For example, by performance of logic operations (forexample, AND operations) performed based on outputs of an (N-1)^(th)shift register and an N^(th) shift register in the driver circuit, a newtiming signal can be generated in an extremely simple structure.Furthermore, by the number of the stage of a selected shift registerbeing changed as appropriate, a great variety of timing signals can begenerated in a fairly simple structure. Alternatively, timing signalsmay be generated by frequency divider circuits and the like beingcombined together as appropriate.

Next, a luminance L in one luminance detection period is detected (StepS606). Then, the luminance L detected during one luminance detectionperiod is compared to a threshold value I per luminance detectionperiod, I/K (Step S608). When the detected luminance L exceeds thethreshold value I per luminance detection period, I/K (or is greaterthan or equal to I/K), the process proceeds to the next step. When suchis not the case, a luminance L′ is detected during the next luminancedetection period, and the same type of comparison is made (Step S606,Step S608). Here, I/K is used as the object of comparison because I is athreshold value that is set based on the target luminance H and I/K isrepresented as the integral value of one frame period. Meanwhile, anintegration period in detection of the luminance L is 1/K of one frameperiod.

Next, a difference in luminance δL is detected from the luminance Lduring one luminance detection period and a luminance L″ during aprevious luminance detection period (Step S610). Then, the difference inluminance δL is compared to the threshold value J per luminancedetection period, J/K (Step S612). When the difference in luminance δLis smaller than the threshold value J per luminance detection period,J/K (or is less than or equal to J/K), the backlight is turned on atthat timing (Step S614). When such is not the case, the process returnsto Step S606, and the same steps are repeated one more time. Here, J/Kis used as the object of comparison because J is a threshold value thatis set based on the target luminance H and J/K is represented as theintegral value of one frame period. Meanwhile, because the difference inluminance δL is a difference in luminance during one luminance detectionperiod, an integration period is 1/K of one frame period.

It is to be noted that in the block diagram of a control circuit shownin FIG. 5, the configuration is set to be one in which the comparisonfor the threshold value I and the comparison for the threshold value Jare performed in parallel, and then, results thereof are judged;however, in actual performance, the process is just like that show bythe flow in FIG. 6. In the flow in FIG. 6, for sake of simplicity, aconfiguration is shown in which the comparison for the threshold value Iis performed and then the comparison for the threshold value J isperformed; however, the configuration may be set to be one in which thecomparison for the threshold value J is performed first and then thecomparison for the threshold value I is performed, or the configurationmay be set to be that of the parallel type of flow illustrated in FIG.5.

It is to be noted that, in the present embodiment mode, operations ofpixels in a monitor section may be performed separately from operationsof pixels in a display section, or the operations of pixels in thedisplay section may be performed simultaneous with the operations ofpixels in a monitor section. In cases in which the operations of pixelsin the monitor section are performed simultaneous with the operations ofpixels in the display section, it is preferable that operations be madeto be performed simultaneously with respect to the last pixel in themonitor section to which a signal is written. By operations being madeto be performed simultaneously with respect to the last pixel in themonitor section to which a signal is written, the timing at which theresponse of the liquid crystal in all pixels on the screen is completedbecomes easy to calculate. In cases in which the operations of thepixels in the monitor section are performed separately from theoperations of the pixels in the display section, the timing for thebacklight being switched on and off may be corrected as appropriate.

As described above, timing for the backlight being switched on and offcan be set according to the flow shown in FIG. 6. The set timing isstored in memory and can be used for a given continuous period of time.Of course, the structure may also be set to be one in which the timingof the backlight being switched on and off is changed for each frameperiod.

FIG. 7 is a graph showing a relationship between luminance(instantaneous luminance) and timing for the backlight being turned onfor cases in which the switching timing control method for control ofthe timing of the backlight being switched on and off shown in thepresent embodiment mode is used. The vertical axis in the graphrepresents luminance when the target luminance is set to be 100. Thehorizontal axis represents luminance detection periods for one frameperiod (from a first luminance detection period to a thirtieth luminancedetection period). In FIG. 7, luminance greater than or equal to thethreshold value is represented in a region 700, and a period duringwhich the backlight is turned on is represented in a region 702. Longarrows in the graph indicate that it has been determined that theluminance has exceeded the threshold value for periods from the arrowsonward (for periods from a fourteenth luminance detection period); shortarrows in the graph indicate that, for periods prior to that (that is,for periods prior to the sixteenth luminance detection period), theamount of difference in luminance has dropped below the threshold value.In the present embodiment mode, a case in which the threshold value ofthe luminance is set to be 95% of the target luminance and one frameperiod is divided up into 30 luminance detection periods is shown;however, the present invention is not to be taken as being limited tothis configuration. Various parameters can be changed as appropriate.

In the case of FIG. 7, an extremely large noise component 704 is presentin a transient response period of the liquid crystal. However, this doesnot cause major problems with backlight control in the liquid crystaldisplay device of the present embodiment mode. Even though the state isone in which the luminance exceeds the threshold value, the reason whyproblems do not occur with backlight control is because comparison ofthe difference in luminance with a threshold value is performed inaddition to comparison of the luminance with a threshold value. Forcomparison of the luminance with a threshold value and comparison of thedifference in the luminance with a threshold value, so to speak, twodifferent kinds of filters are used to detect optimal timing. Asdescribed in the present embodiment mode, by combination of differentmethods to remove the noise component, backlight control of an evenhigher level of accuracy comes to be possible. Of course, a method thatcan be used as a filter is not to be taken as being limited to themethod described in the present embodiment mode. For example, asdescribed in Embodiment Mode 2, noise may be eliminated by addition of anew condition, which is that “the backlight is to be turned on when thedetected luminance exceeds the threshold value at least two times (ormore than two times) in a row.” Furthermore, three or more differentmethods may also be used in combination with each other.

In the case of FIG. 7, as with the case of FIG. 4 in Embodiment Mode 2,timing at which conditions are fulfilled and timing of the backlightbeing turned on are not exactly equal to each other. However, asdescribed in Embodiment Mode 2, this problem may be solved by the lengthof a luminance detection period, which is an integration period, beingshortened enough (that is, by one frame period being divided up into anumber of luminance detection periods). Of course, this kind of problemmay be solved, not by use of luminance determined by time integration,but rather, by the structure being set to be one in which determinationis performed using instantaneous luminance. Furthermore, in cases inwhich the timing of control of the backlight is retained in memory andconstant control is performed for a given period of time at the sametiming, a correction is added as appropriate (in the case of FIG. 7, thetiming for the backlight being turned on is switched from being duringthe sixteenth luminance detection period to being during the fifteenthluminance detection period), and the timing for the backlight beingturned on can be optimized even more.

It is to be noted that, in the present embodiment mode, a case in whichthe case of the luminance being changed from a state of low luminance toa state of high luminance is set to be a test pattern is described;however, the present invention is not to be taken as being limited tothis case only. The present invention can also be used in a structure inwhich the case of the luminance being changed from a state of highluminance to a state of low luminance is set to be a test pattern. Inthis case, different parameters may be changed as appropriate.

As described above, by performance of control of the switching of thebacklight using a light sensor, the realization of impulse driving byoptimal timing becomes possible. Herewith, video performance is improveddramatically. Furthermore, even in cases in which the response of theliquid crystal changes with changes in the environment (temperature,pressure, and the like), because optimal impulse driving can berealized, the video performance can be maintained in a high stateconstantly. In addition, because temperature sensors and the like usedto detect changes in the environment become unnecessary and there is noneed to use a reference table (a so-called lookup table) for control ofthe switching of the backlight, structures of sensors, memory, and thelike can be simplified.

It is to be noted that impulse driving for cases in which the presentinvention is used is different from impulse driving in the conventionalmeaning. That is, while conventional impulse driving refers to luminancefocused on one pixel changing in a pulse-like manner, impulse drivingrealized by use of the present invention refers to luminance of pixelsof one screen changing simultaneously and in a pulse-like manner. Tofurther reiterate, while conventional impulse driving is impulse drivingby point-sequential driving or line-sequential driving, impulse drivingrealized by use of the present invention has a kind of aspect of pixelsfor one screen being turned on simultaneously, a “frame-sequentialdriving” kind of aspect. Because all pixels for one screen can be turnedon simultaneously, video performance can be dramatically improved. It isto be noted that, to realize the above-described impulse driving, thelength of an intended period (one frame period in the present embodimentmode) needs to be longer than the sum of the length of time needed forwriting of a signal to all pixels and the length of time needed forcompletion of the response of the liquid crystal of all pixels. This isattributed to the fact that turning on of the backlight starts from astate in which the response of the liquid crystal of all pixels iscompleted. However, in view of improvements in processing capability ofdriver circuits, improvements in the response speed of a liquid crystal,and the like in recent years, this point does not cause any problems inparticular.

In addition, even in states in which no time passes from input ofelectricity and in states in which a constant period of time passes frominput of electricity, a liquid crystal display device exhibiting highvideo performance can be provided. Furthermore, high video performancecan be obtained even in display panels on streets that are subject tohostile environments, cellular phones, car electronics, and the like.

Furthermore, in the liquid crystal display device of the presentembodiment mode, timing of the backlight being turned on is controlledusing two types of different conditions. Herewith, control of anextremely high level of accuracy with effects of noise and the likeremoved comes to be possible. That is, high-level video performancebecomes possible to be provided stably.

It is to be noted that, in the present embodiment mode, a description isgiven for cases in which control of switching of a backlight isperformed; however, the present invention can be used in cases otherthan in cases in which control of switching of a backlight is performed.For example, the present invention can also be used to determine optimalvoltage in overdriving. In this case, by overdrive voltage beingcontrolled so that display is performed at a target luminance by adesired period, video performance can be improved dramatically. Ofcourse, control of overdrive voltage and control of switching of thebacklight may be used in combination with each other.

Furthermore, in the present embodiment mode, an example is given inwhich processing is performed using hardware; however, the presentinvention is not to be taken as being limited to this configuration.Because a technical idea of the present embodiment mode is that controlof switching of a backlight is performed based on information obtainedfrom a light sensor, any type of structure can be employed as long as itis a structure in which this technical idea can be implemented. Forexample, processing performed using hardware in the present embodimentmode can also be performed using software.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 2, as appropriate. It is to benoted that the output control of the output of a backlight shown inEmbodiment Mode 1 and control of switching of a backlight in the presentembodiment mode can be used in combination with each other. By thestructures being used in combination with each other, a liquid crystaldisplay device with excellent image quality and high video performanceis realized.

Embodiment Mode 4

In the present embodiment mode, another example of a liquid crystaldisplay device and a driving method thereof of the present inventionwill be described using FIG. 8.

Because the structure of a panel that can be used in a liquid crystaldisplay device of the present invention is the same as that ofEmbodiment Mode 1, a detailed description thereof will be omitted here.In the present embodiment mode, a case in which a combination of anoutput (luminance) control method of a backlight of Embodiment Mode 1and a switching control method of a backlight of Embodiment Mode 2 orEmbodiment Mode 3 is used will be described hereinafter.

FIG. 8 is an example of a case in which a combination of an output(luminance) control method of a backlight and a switching control methodof a backlight is used. It is to be noted that, for a circuit structure,because the circuit structures given in any of Embodiment Mode 1 toEmbodiment Mode 3 can be used together in combination, a detaileddescription thereof will be omitted here. It is to be noted that thecircuit structure of the present embodiment mode is not to be taken asbeing limited to being a combination of the circuit structures ofEmbodiment Mode 1 to Embodiment Mode 3, and a circuit structure that hasthe same functions can be used as appropriate. Furthermore, a circuitthat can be used in common when a combination of the circuit structuresof Embodiment Mode 1 to Embodiment Mode 3 is used may be used in common.For example, the structure may be set to be one in which an integratedcircuit is used in common.

In the present embodiment mode, a structure in which, at first, controlof output of a backlight is performed and then control of switching of abacklight is performed will be described. Of course, the structure maybe set to be one in which, at first, control of switching of a backlightis performed and then control of output of a backlight is performed, aswell. It is to be noted that because reference can be made to EmbodimentMode 1 to Embodiment Mode 3 in regard to details of each of theoperations of control of output of a backlight and control of switchingof a backlight, such details will be omitted here.

First, lighting of a backlight and a light source for monitor use isstarted. At the same time, driving of a liquid crystal in a pixel formonitor use is performed using a monitor pattern (Step S800). Here, incases in which the backlight and the light source for monitor use areprovided separately from each other, lighting of the backlight andlighting of the light source for monitor use may both be started at thesame time. Then, luminance is detected by a light sensor (Step S802),and control of the output of the backlight is performed using thedetected luminance (Step S804).

Next, the detected luminance and a target luminance are compared (StepS806). Here, in cases in which the target luminance is not reached, thesame steps are repeated during a subsequent period. It is to be notedthat the length of a unit period during which output of the backlight isto be controlled may be equal to the length of one frame period orlonger than the length of one frame period. Moreover, the unit periodmay be set to be a period that is shorter than one frame period, aswell. In cases in which the target luminance is reached, for control ofswitching of the backlight, detection of the optical response of theliquid crystal is started (Step S808).

Next, control of the backlight being switched on and off is performedaccording to the detected optical response (Step S810). In cases inwhich the control of the backlight being switched on and off iscompleted, the step for the control of the output of the backlight isagain performed.

It is to be noted that, in the present embodiment mode, the structure isset to be one in which control of the output of the backlight isperformed again after control of the backlight being switched on and offis completed; however, the present invention is not limited to havingthis structure only. The structure may also be set to be one in which,after control of the backlight being switched on and off is completed,control of the output of the backlight is performed after a given amountof time has passed. By repeated performance of control of the output ofthe backlight and control of the backlight being switched on and offduring a short period of time, the liquid crystal display device can bemaintained at an optimal state constantly. On the other hand, by controlof the output and control of the switching being performed again after agiven amount of time has passed, the number of times of operation of acircuit used for control can be decreased while the liquid crystaldisplay device is maintained at a favorable condition. That is, powerconsumption can be reduced while excellent image quality and high videoperformance are maintained.

Moreover, in view of characteristics of the present invention, bycombination of a liquid crystal material by which a high viewing anglecan be realized with a driving method (for example, a VA method, an IPSmethod, or the like) by which a high viewing angle can be realized, evenmore superior image quality can be provided. In addition, by use of aliquid crystal material that has a fast response speed with a drivingmethod (for example, an OCB method or the like) that has a fast responsespeed, even high video performance can be obtained.

As described above, by performance of control of the output (luminance)of the backlight and control of the switching of the backlight using alight sensor, impulse driving by optimal timing can be realized whiledesired luminance is displayed accurately. Herewith, a liquid crystaldisplay device with excellent image quality and high video performancecan be provided. Furthermore, even in cases in which the response speedof the liquid crystal changes with changes in the environment(temperature, pressure, and the like), optimal impulse driving can berealized while the desired luminance is maintained. Thus, excellentimage quality and high video performance can be provided under anycircumstances. In addition, because temperature sensors and the likeused to detect changes in the environment become unnecessary and thereis no need to use a reference table (a so-called lookup table) fromwhich to refer in regard to the relationship between temperature, andthe like, and luminance, structures of sensors, memory, and the like canbe simplified.

It is to be noted that impulse driving for cases in which the presentinvention is used is different from impulse driving in the conventionalmeaning. That is, while conventional impulse driving refers to luminancefocused on one pixel changing in a pulse-like manner, impulse drivingrealized by use of the present invention refers to luminance of pixelsof one screen changing simultaneously and in a pulse-like manner. Tofurther reiterate, while conventional impulse driving is impulse drivingby point-sequential driving or line-sequential driving, impulse drivingrealized by use of the present invention has a kind of aspect of pixelsfor one screen being turned on simultaneously, a “frame-sequentialdriving” kind of aspect. Because all pixels for one screen can be turnedon simultaneously, video performance can be dramatically improved.

In addition, even in states in which no time passes from input ofelectricity and in states in which a constant period of time passes frominput of electricity, excellent image quality and high video performancecan be provided. Furthermore, excellent image quality and high videoperformance can be obtained even in display panels on streets that aresubject to hostile environments, cellular phones, car electronics, andthe like.

It is to be noted that, in the present embodiment mode, a description isgiven for cases in which control of switching of a backlight isperformed; however, the present invention can be used in cases otherthan in cases in which control of switching of a backlight is performed.For example, the present invention can also be used to determine optimalvoltage in overdriving. In this case, by overdrive voltage beingcontrolled so that display is performed at a target luminance by adesired period, video performance can be improved dramatically. Ofcourse, control of overdrive voltage and control of switching of thebacklight may be used in combination with each other.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 3, as appropriate.

Embodiment Mode 5

In the present embodiment mode, a liquid crystal display device with astructure differing from that of the liquid crystal display device shownin Embodiment Mode 1 will be described using FIGS. 9A and 9B and FIGS.10A to 10D.

The structure shown in FIGS. 1A and 1B of Embodiment Mode 1 is that of acase in which luminance of a backlight or of a light source for monitoruse is detected by a light sensor, and the case is assumed to be one inwhich the backlight and the light source for monitor use are provided onthe same side (specifically, below the polarizing plate 120 a) as theliquid crystal layer. On the other hand, in FIGS. 9A and 9B, a structurein which the backlight is on one side of a liquid crystal layer and thelight source for monitor use is on the other side of the liquid crystallayer is shown. It is to be noted that, for cases in which the structureshown in FIGS. 9A and 9B is used, an important point that needs to betaken into account is that there is a need for the backlight and thelight source for monitor use to be provided separately from each other.

FIG. 9A shows a planar-view diagram of a panel. With regard to theplanar-view diagram, the structure is about the same as the structureshown in FIGS. 1A and 1B. A substrate 900 and a counter substrate 910are bonded together by a sealant 912. Furthermore, a pixel section 902,a scanning line driver circuit 904 a, a scanning line driver circuit 904b, a signal line driver circuit 906, and a monitor section 908 areprovided between the substrate 900 and the counter substrate 910.Signals from external are input via a flexible printed circuit (an FPC)914.

FIG. 9B is a diagram in which a simplified stacked-layer structure ofthe panel shown in FIG. 9A is shown. A liquid crystal layer 922 isprovided between the substrate 900 and the counter substrate 910.Furthermore, a polarizing plate 920 a and a polarizing plate 920 b areprovided on an outer side of the substrate 900 and an outer side of thecounter substrate 910 (the lower side of the substrate 900 and the upperside of the counter substrate 910 in the diagram), respectively. Abacklight 924 and a light sensor 926 are provided on the outer side ofthe polarizing plate 920 a (on the lower side of the polarizing plate920 a), and a light source 928 for monitor use is provided on the outerside of the polarizing plate 920 b (on the upper side of the polarizingplate 920 b).

The light sensor 926 detects light that passes through the polarizingplate 920 b, the counter substrate 910, the liquid crystal layer 922,the substrate 900, and the polarizing plate 920 a in the order given.Herewith, changes in the luminance of the backlight occurring withchanges in the environment (for example, changes in temperature,pressure, and the like) and the length of time for response of theliquid crystal are calculated, whereby control of the backlight (forexample, control of the luminance, control of the timing of switching,and the like of the backlight) can be performed. In FIGS. 9A and 9B, astructure is shown in which the light sensor 926 and the backlight 924are provided in the same layer; however, the present invention is notlimited to having this structure. The light sensor 926 may be placed insuch a way that light from the backlight 924 is not detected.Furthermore, in FIGS. 9A and 9B, the structure is one in which thebacklight 924 has a notch in one part; however, the present invention isnot to be taken as being limited to having this structure.

For the light source for monitor use, it is preferable that a lightsource that has the same characteristics as those of the backlight beused; however, if the luminance of the light source for monitor use andthe luminance of the backlight are to have a correspondencerelationship, then the present invention is not to be taken as beinglimited to use of a light source with the same characteristics as thoseof the backlight. It is to be noted that, in FIG. 9B, a structure inwhich light is extracted from a counter substrate side is shown;however, the present invention can be used in a liquid crystal displaydevice with a structure in which light is extracted from a substrate(active matrix substrate) side in the same way. In this case, the lightsensor is to detect light that passes through a polarizing plate, asubstrate (an active matrix substrate), a liquid crystal layer, acounter substrate, and a polarizing plate in the order given.

It is to be noted that, for an example of a structure resembling thestructure of FIGS. 9A and 9B, there is a structure in which light fromexternal (external light) is used instead of the light source formonitor use. If light from external is detected by a light sensor, theluminance of the backlight can be adjusted in response to the brightnessof the surroundings. It is to be noted that, in achievement of thisobjective, the structure may be any kind of structure as long as it isone in which the light sensor can detect light from external and is notto be taken as being limited to being a structure similar to thestructure shown in FIGS. 9A and 9B. In addition, in conditions in whichthe light from external is stable, control of switching of the backlightcan also be performed using the light from external in the calculationof the time needed for response of the liquid crystal.

Next, examples of placement of a monitor section in a liquid crystaldisplay device are shown in FIGS. 10A to 10D. FIGS. 10A to 10C arediagrams showing examples of placement of a monitor section in a liquidcrystal display device in which a small-sized panel is used. FIG. 10D isa diagram showing an example of placement of a monitor section in aliquid crystal display device in which a large-sized panel is used. Itis to be noted that a housing 1000 and a display section 1002 areindicated using the same reference numerals in each of FIGS. 10A to 10D.

FIG. 10A shows an example of a structure in which a monitor section 1010and a monitor section 1012 are provided. A light sensor is provided ineach of the monitor section 1010 and the monitor section 1012. Due tothere being two monitor sections, luminance detection for output controland luminance detection for switching control can be performed usingdifferent light sensors. That is, output control and switching controlcan be performed separately, or output control and switching control canbe performed simultaneously. In cases in which output control andswitching control are performed simultaneously, because the length of aperiod of time needed for control can be shortened compared to that ofcases in which output control and switching control are performedalternatingly, control can be performed even more finely.

FIG. 10B shows an example of a structure in which a monitor section1020, a monitor section 1022, a monitor section 1024, and a monitorsection 1026 are provided. A light sensor is provided in each of themonitor section 1020, the monitor section 1022, the monitor section1024, and the monitor section 1026. The monitor section 1020 and themonitor section 1024 are monitor sections used for performance ofluminance detection for output control, and the monitor section 1022 andthe monitor section 1026 are monitor sections used for performance ofluminance detection for switching control. By performance of luminancedetection for output control and luminance detection for switchingcontrol using two light sensors for each, the accuracy of the luminancedetection can be improved. In FIG. 10B, an example is shown in whichluminance detection for output control and luminance detection forswitching control are performed using two monitor sections for each;however, the structure may be set to be one in which luminance detectionis performed using three or more monitor sections for each, as well.

FIG. 10C shows an example of a structure in which a monitor section1030, a monitor section 1032, and a monitor section 1034, are provided.A light sensor is provided in each of the monitor section 1030, themonitor section 1032, and the monitor section 1034. In addition, anopening is provided in a region corresponding to that of the monitorsection 1034 of the housing 1000. The monitor section 1030 is a monitorsection used for performance of luminance detection for output control,and the monitor section 1032 is a monitor section used for performanceof luminance detection for switching control. Light from external isdetected by the monitor section 1034. By provision of the monitorsection 1034, the luminance of the backlight can be adjusted in responseto the brightness of the surroundings. Furthermore, in conditions inwhich the light from external is stable, control of switching of thebacklight can also be performed using the light from external in thecalculation of the time needed for response of the liquid crystal.

In a liquid crystal display device of FIG. 10D, a monitor section 1040is provided. A light sensor is provided in the monitor section 1040. Ina large-sized liquid crystal display device such as the one shown inFIG. 10D, changes in the surrounding environment are more moderatecompared with the kind of liquid crystal display devices used inportable devices and the like. Consequently, the structure may also beset to be one in which the number of monitor sections is minimized. Ofcourse, fine control may be performed by provision of a plurality ofmonitor sections, as well.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 4, as appropriate.

Embodiment Mode 6

In the present embodiment mode, an example of a light sensor in whichthe present invention is used will be described using FIGS. 11A and 11B.Specifically, an example of a structure of a photo IC will be described.

A photo IC 1100 shown in FIG. 11A has a photoelectric conversion element1102 and an integrated circuit that is formed of transistors; it ispreferable that the integrated circuit have a structure that has acurrent mirror circuit 1108 that is formed of at least a transistor 1104and a transistor 1106 that is connected to a diode. It is to be notedthat, in the present embodiment mode, the transistors of which thecurrent mirror circuit 1108 is formed may be either n-channeltransistors or p-channel transistors, but an example in which thetransistors are n-channel transistors is given here. In addition, aphoto IC is also referred to as a photoelectric device.

A terminal 1110 is connected to a gate electrode and a first electrode(either a source electrode or drain electrode) of the transistor 1106via the photoelectric conversion element 1102, and a second electrode(the other one of either the source electrode or drain electrode) of thetransistor 1106 is connected to a terminal 1112. Furthermore, theterminal 1110 is also connected to a first electrode (either a sourceelectrode or drain electrode) of the transistor 1104. Meanwhile, asecond electrode (the other one of either the source electrode or drainelectrode) of the transistor 1104 is connected to the terminal 1112. Itis to be noted that a gate electrode of the transistor 1104 is connectedto the gate electrode of the transistor 1106.

In the photo IC 1100, electrons and holes are generated when thephotoelectric conversion element 1102 is irradiated with light, wherebyan electric current is produced. It is to be noted that the currentmirror circuit 1108 operates to amplify the amount of electric currentobtained from the photoelectric conversion element 1102. In the photo IC1100 shown in the present embodiment mode, a case is given in whichthere is one transistor 1104, that is, a case in which the amount ofelectric current obtained from the photoelectric conversion element 1102is amplified by twice as much; however, for cases in which an evengreater amount of electric current is desired to be obtained, aplurality of units 1114, which are each formed of the transistor 1104the gate electrode of which is connected to the gate electrode of thetransistor 1106, may be provided connected together in parallel betweenthe terminal 1110 and the terminal 1112. For example, by the number ofthe units 1114 being set to be n, the photo IC 1100 can be made tooutput approximately twice (n+1) as much electric current as an electriccurrent I obtained from the photoelectric conversion element 1102. It isto be noted that because the amount of electric current obtained fromthe photoelectric conversion element 1102 depends on the amount ofilluminance, the amount of illuminance, that is, the amount ofirradiated light, becomes able to be detected.

Next, a structure of the photoelectric conversion element 1102 will bedescribed with reference to FIG. 11B.

FIG. 11B is a diagram showing a simplified of a stacked-layer structureof the photoelectric conversion element 1102. The photoelectricconversion element 1102 is formed by a conductive film that transmitslight, a first conductive semiconductor layer, an intrinsic layer (anintrinsic semiconductor layer), and a second conductive semiconductorlayer being stacked together in the order given over a substrate thattransmits light. Specifically, a conductive film 1152 that transmitslight, a p-type semiconductor layer 1154, an intrinsic layer 1156, ann-type semiconductor layer 1158, and a back electrode 1160 are stackedtogether in the order given over a substrate 1150 that transmits light.

For the substrate 1150 that transmits light, substrates in whichinsulating materials are used can be given. For example, a glasssubstrate of barium borosilicate glass, aluminum borosilicate glass, orthe like; a quartz substrate; a stainless steel substrate; or the likecan be used. Furthermore, a flexible substrate formed of a syntheticresin such as a plastic typified by PET, PES, or PEN; acrylic; or thelike can be used, as well. It is to be noted that, in view of propertiesof the photoelectric conversion element, it is desired that thesubstrate that transmits light have a property by which desired light istransmitted.

The conductive film 1152 that transmits light can be formed by asputtering method or the like using a material that transmits light suchas indium tin oxide (ITO), indium tin oxide that contains silicon oxide,zinc oxide (ZnO), tin oxide (SnO₂), or the like. For thickness, it ispreferable that the thickness of the conductive film 1152 that transmitslight be 1 μm or less. It is to be noted that, needless to say, it isdesired that the conductive film 1152 that transmits light also have aproperty by which desired light is transmitted.

The p-type semiconductor layer 1154, the intrinsic layer 1156, and then-type semiconductor layer 1158 can each be formed using a plasma CVDmethod or the like. For conductive materials, using materials in whichsilicon (Si) is set to be the main component is preferable; however,materials that can be used are not limited to being silicon. Materialscan be selected as appropriate based on desired characteristics. In thep-type semiconductor layer 1154, boron or the like is used as a dopant,and in the n-type semiconductor layer 1158, phosphorus or the like isused as a dopant.

The back electrode 1160 can be formed by a CVD method, a sputteringmethod, an evaporation method, or the like using a metal element such astantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), chromium(Cr), aluminum (Al), gold (Au), silver (Ag), copper (Cu), platinum (Pt),niobium (Nb), or the like or an alloy material or a compound materialcontaining one or more of these metal elements. For thickness, it ispreferable that the thickness of the back electrode 1160 be 100 μm orless.

It is to be noted that the structure of the photoelectric conversionelement 1102 shown in FIG. 11B is merely one example, and the presentinvention is not to be taken as being limited to this structure only. Aphotoelectric conversion element in which changes, additions, or thelike are made to the stacked-layer structure can be used, as well.

Furthermore, for the structure of the photo IC, as well, the structureis not to be taken as being limited to that shown in FIG. 11A. A photoIC with a structure that does not have a current mirror circuit may beused, or a photo IC with a structure other than this kind of structuremay be used. Moreover, the structure of the photoelectric conversionelement used in the photo IC is not limited to being the structure givenin the present embodiment mode.

In addition, because a photo IC is only one example of a light sensor,another type of light sensor can also be used to realize the presentinvention. For example, a photomultiplier tube or the like can also beused for the light sensor.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 5, as appropriate.

Embodiment Mode 7

Examples of a fabrication method of a semiconductor substrate that canbe used in a liquid crystal display device of the present invention willbe described using FIGS. 12A to 12D, FIGS. 13A to 13C, and FIGS. 14A to14C. It is to be noted that cases in which a crystalline semiconductorfilm is used will be described in the present embodiment mode; however,an amorphous semiconductor film or a single-crystal semiconductor filmmay be used, as well.

First, as shown in FIG. 12A, a base film 1202 is formed over a substrate1200. For the substrate 1200, for example, a glass substrate of bariumborosilicate glass, aluminum borosilicate glass, or the like; a quartzsubstrate; a stainless steel substrate; or the like can be used.Furthermore, a flexible substrate formed of a synthetic resin such as aplastic typified by PET, PES, or PEN; acrylic; or the like can also beused.

The base film 1202 is provided to prevent an alkali metal, such as Na orthe like, or an alkaline earth metal contained within the substrate 1200from diffusing into a semiconductor film and imparting adverse effectson the characteristics of a semiconductor element. Consequently, thebase film 1202 is formed using an insulating material of silicon nitrideor silicon oxide that contains nitrogen by which the diffusion of analkali metal or alkaline earth metal into a semiconductor film can besuppressed. In the present embodiment mode, a silicon oxide film thatcontains nitrogen is formed for the base film 1202 so as to have a filmthickness greater than or equal to 10 nm and less than or equal to 400nm (preferably, greater than or equal to 50 nm and less than or equal to300 nm) using a plasma CVD method.

Next, a semiconductor film 1204 is formed over the base film 1202. Thefilm thickness of the semiconductor film 1204 is set to be greater thanor equal to 25 nm and less than or equal to 100 nm (preferably, greaterthan or equal to 30 nm and less than or equal to 60 nm). It is to benoted that the semiconductor film 1204 may be formed of an amorphoussemiconductor or a polycrystalline semiconductor. In addition, for thesemiconductor, not only silicon (Si) but also silicon germanium (SiGe)or the like can be used. When silicon germanium is used, it ispreferable that the concentration of germanium be greater than or equalto 0.01 at. % approximately and less than or equal to 4.5 at. %approximately.

Next, as shown in FIG. 12B, crystallization is performed by irradiationof the semiconductor film 1204 with a linear laser beam 1208. If lasercrystallization is performed as in the present embodiment mode, in orderto increase the tolerance of the semiconductor film 1204 to a laserbeam, a heat treatment step performed at a temperature of 500° C. forone hour may be added before the laser crystallization step.

In the laser crystallization step, for example, a continuous wave laser(a CW laser), a quasi-continuous wave laser (a pulsed laser with arepetition rate of 10 MHz or more, preferably, 80 MHz or more), or thelike can be used.

Specifically, for a continuous wave laser, an Ar laser, a Kr laser, aCO₂ laser, a YAG laser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, aGdVO₄ laser, a Y₂O₃ laser, a ruby laser, an alexandrite laser, aTi:sapphire laser, a helium-cadmium laser, and the like can be given.

Furthermore, for a quasi-CW laser, a pulsed laser such as an Ar laser, aKr laser, an excimer laser, a CO₂ laser, a YAG laser, a YVO₄ laser, aYLF laser, a YAlO₃ laser, a GdVO₄ laser, a Y₂O₃ laser, a ruby laser, analexandrite laser, a Ti:sapphire laser, a copper vapor laser, or a goldvapor laser can be given.

This kind of pulsed laser comes to exhibit the same effects as acontinuous wave laser if the repetition rate is increased.

For example, when a solid-state laser capable of continuous oscillationis used, by irradiation at the second through fourth harmonics of afundamental frequency, crystals with a large grain size can be obtained.Typically, the second harmonic (532 nm) or third harmonic (355 nm) of aYAG laser (a fundamental of 1064 nm) can be used. The power density maybe set to be greater than or equal to 0.01 MW/cm² and less than or equalto 100 MW/cm² (preferably, greater than or equal to 0.1 MW/cm² and lessthan or equal to 10 MW/cm²).

As described above, by irradiation of the semiconductor film 1204 with alaser beam, a crystalline semiconductor film 1210 with even highercrystallinity is formed.

Next, by etching of the crystalline semiconductor film 1210 as selected,as shown in FIG. 12C, island-shaped semiconductor films 1212, 1214, and1216 are formed.

Next, an impurity element is introduced into each of the island-shapedsemiconductor films 1212, 1214, and 1216 in order to control thresholdvoltage. In the present embodiment mode, boron (B) is introduced bydoping with diborane (B₂H₆).

Next, an insulating film 1218 is formed so as to cover the island-shapedsemiconductor films 1212, 1214, and 1216. For the insulating film 1218,for example, silicon oxide, silicon nitride, silicon oxide that containsnitrogen (SiO_(x)N_(y), where x>y>0), or the like can be used.Furthermore, for a film formation method, a plasma CVD method, asputtering method, or the like can be used.

Next, after a first conductive film 1220 and a second conductive film1222 are formed over the insulating film 1218, gate electrodes 1236,1238, and 1240 are formed by selective etching of the first conductivefilm 1220 and the second conductive film 1222 (FIG. 12D and FIGS. 13A to13C).

For the first conductive film 1220 and second conductive film 1222, oneor a plurality of elements selected from aluminum (Al), tantalum (Ta),titanium (Ti), molybdenum (Mo), tungsten (W), neodymium (Nd), chromium(Cr), nickel (Ni), platinum (Pt), gold (Au), silver (Ag), copper (Cu),magnesium (Mg), scandium (Sc), cobalt (Co), zinc (Zn), niobium (Nb),silicon (Si), phosphorus (P), boron (B), arsenic (As), gallium (Ga),indium (In), and tin (Sn); a compound or alloy material that containsone of the given elements as its main component (for example, indium tinoxide (ITO), indium zinc oxide (IZO), indium tin oxide that containssilicon oxide (ITSO), zinc oxide (ZnO), aluminum-neodymium (Al—Nd),magnesium-silver (MgAg), or the like); a material that is a combinationof any of these compounds; or the like can be used. In addition to whatis given above, a silicide (for example, aluminum-silicon,molybdenum-silicon, or nickel silicide), a compound that containsnitrogen (for example, titanium nitride, tantalum nitride, or molybdenumnitride), silicon (Si) that has been doped with an impurity element suchas phosphorus (P) or the like, or the like may be used. It is to benoted that in the present embodiment mode, the structure of conductivefilms is set to be a two-layer structure of the first conductive film1220 and the second conductive film 1222, but the structure may be asingle layer or a stacked-layer structure of three or more layers, aswell.

In the present embodiment mode, the gate electrodes 1236, 1238, and 1240are formed as described hereinafter. First, for the first conductivefilm 1220, for example, a tantalum nitride film is formed at a filmthickness greater than or equal to 10 nm and less than or equal to 50nm, typically, at a film thickness of 30 nm. In addition, for the secondconductive film 1222 formed over the first conductive film 1220, forexample, a tungsten film is formed at a film thickness of greater thanor equal to 200 nm and less than or equal to 400 nm, typically, at afilm thickness of 370 nm, and a stacked-layer film of the firstconductive film 1220 and the second conductive film 1222 is formed (FIG.12D).

Next, the second conductive film 1222 is patterned by anisotropicetching, whereby upper layer gate electrodes 1224, 1226, and 1228 areformed (FIG. 13A). Subsequently, the first conductive film 1220 ispatterned by isotropic etching, whereby bottom layer gate electrodes1230, 1232, and 1234 are formed (FIG. 13B). The gate electrodes 1236,1238, and 1240 are formed by the aforementioned steps.

The gate electrodes 1236, 1238, and 1240 may each be formed as a part ofa gate wiring, or the structure may be one in which the gate electrodes1236, 1238, and 1240 are connected to a gate wiring that is formedseparately.

Next, an impurity imparting a conductivity (either n-type or p-typeconductivity) is added to each of the island-shaped semiconductor films1212, 1214, and 1216 using the gate electrodes 1236, 1238, and 1240; aresist formed as selected; and the like as masks, whereby sourceregions, drain regions, low-concentration impurity regions, and the likeare formed.

First, phosphorus (P) is added to the island-shaped semiconductor films1212 and 1216 using phosphine (PH₃). For introduction conditions, it ispreferable that the accelerating voltage be set to be greater than orequal to 60 kV and less than or equal to 120 kV and that the dose amountbe set to be greater than or equal to 1×10¹³ atoms·cm⁻² and less than orequal to 1×10¹⁵ atoms·cm⁻². By introduction of this impurity, channelformation regions 1242 and 1248 of n-channel TFTs 1278 and 1282 that areto be formed in a later step are formed (FIG. 13C).

Moreover, boron (B) is added to the island-shaped semiconductor film1214 using diborane (B₂H₆). For introduction conditions, it ispreferable that the applied voltage be set to be greater than or equalto 60 kV and less than or equal to 100 kV and that the dose amount beset to be greater than or equal to 1×10¹³ atoms·cm⁻² and less than orequal to 5×10¹⁵ atoms·cm². Hereby, each of a source region or drainregion 1244 and a channel formation region 1246 of a p-channel TFT 1280that is to be formed in a later step are formed (FIG. 13C).

Next, gate insulating films 1250, 1252, and 1254 are formed by selectiveetching of the insulating film 1218.

After the gate insulating films 1250, 1252, and 1254 are formed,phosphorus (P) is introduced into the island-shaped semiconductor filmsthat form the n-channel TFTs 1278 and 1282 using phosphine (PH₃) at anapplied voltage of greater than or equal to 40 kV and less than or equalto 80 kV and a dose amount of greater than or equal to 1.0×10¹⁵atoms·cm⁻² and less than or equal to 2.5×10¹⁶ atoms·cm⁻². Hereby,low-concentration impurity regions 1258 and 1262 and regions 1256 and1260, each of which is a source region or a drain region, of n-channelTFTs 1278 and 1282 are formed (FIG. 14A).

In the present embodiment mode, the regions 1256 and 1260, each of whichis a source region or a drain region, each contain phosphorus (P) at aconcentration of greater than or equal to 1×10¹⁹ atoms·cm⁻³ and lessthan or equal to 5×10²¹ atoms·cm⁻³. Furthermore, the low-concentrationimpurity regions 1258 and 1262 each contain phosphorus (P) at aconcentration of greater than or equal to 1×10¹⁸ atoms·cm⁻³ and lessthan or equal to 5×10¹⁹ atoms·cm⁻³. In addition, the region 1244, whichis a source region or drain region contains boron (B) at a concentrationof greater than or equal to 1×10¹⁹ atoms·cm⁻³ and less than or equal to5×10²¹ atoms·cm⁻³.

Next, a first interlayer insulating film 1264 is formed so as to coverthe island-shaped semiconductor films 1212, 1214, and 1216 and the gateelectrodes 1236, 1238, and 1240 (FIG. 14B).

It is preferable that the first interlayer insulating film 1264 beformed of a single layer or stacked layer of an insulating film thatcontains silicon, for example, a silicon oxide film, a silicon nitridefilm, a silicon oxide film that contains nitrogen (a film ofSiO_(x)N_(y), where x>y>0), or the like using a plasma CVD method or asputtering method. Of course, the fabrication method and materials ofthe first interlayer insulating film 1264 are not limited to being thosegiven above. For example, a single layer or stacked layer structure ofother insulating films may be used, as well.

Next, a second interlayer insulating film 1266 that functions as aplanarizing film is formed to cover the first interlayer insulating film1264 (FIG. 14C).

For the second interlayer insulating film 1266, a photosensitive ornon-photosensitive organic material (polyimide, acrylic, polyamide,polyimide amide, a resist, or benzocyclobutene), siloxane formed with askeleton structure of bonds of silicon (Si) and oxygen (O) (Si—O—Sibonds), or the like can be used. The second interlayer insulating film1266 may have a single-layer structure or a stacked-layer structure. Fora photosensitive organic material, a positive photosensitive organicresin or negative photosensitive organic resin can be used.

In the present embodiment mode, siloxane is formed for the secondinterlayer insulating film 1266 by a spin-coating method.

Next, the first interlayer insulating film 1264 and the secondinterlayer insulating film 1266 are etched, whereby a contact hole thatreaches the island-shaped semiconductor films 1212, 1214, and 1216 isformed.

It is to be noted that a third interlayer insulating film may be formedover the second interlayer insulating film 1266 and the contact hole maybe formed in the first interlayer insulating film through the thirdinterlayer insulating film, as well. For the third interlayer insulatingfilm, it is preferable that a film through which moisture, oxygen, andthe like do not readily pass be used. Typically, a silicon nitride film,a silicon oxide film, a silicon nitride film that contains oxygen (afilm of SiN_(x)O_(y), where x>y>0 or SiO_(x)N_(y), where x>y>0), a thinfilm that contains carbon as its main component (for example, a DLC filmor a CN film), or the like formed by a sputtering method or a CVD methodcan be used.

Through the contact hole formed in the second interlayer insulating film1266, a third conductive film is formed, and the third conductive filmis etched as selected, whereby electrodes and/or wirings 1268, 1270,1272, 1274, and 1276 are formed.

For the third conductive film, one or a plurality of elements selectedfrom aluminum (Al), tantalum (Ta), titanium (Ti), molybdenum (Mo),tungsten (W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum (Pt),gold (Au), silver (Ag), copper (Cu), magnesium (Mg), scandium (Sc),cobalt (Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus (P),boron (B), arsenic (As), gallium (Ga), indium (In), and tin (Sn); acompound or alloy material that contains one of the given elements asits main component (for example, indium tin oxide (ITO), indium zincoxide (IZO), indium tin oxide that contains silicon oxide (ITSO), zincoxide (ZnO), aluminum-neodymium (Al—Nd), magnesium-silver (MgAg), or thelike); a material that is a combination of any of these compounds; orthe like can be used. In addition to what is given above, a silicide(for example, aluminum-silicon, molybdenum-silicon, or nickel silicide),a compound that contains nitrogen (for example, titanium nitride,tantalum nitride, or molybdenum nitride), silicon (Si) that has beendoped with an impurity element such as phosphorus (P) or the like, orthe like may be used.

In the present embodiment mode, after a titanium (Ti) film, a titaniumnitride film, a silicon-aluminum (Si—Al) alloy film, and a titanium (Ti)film of thicknesses of 60 nm, 40 nm, 300 nm, and 100 nm, respectively,are stacked together, the films are etched as selected so as to beformed into desired shapes, whereby the electrodes and/or wirings 1268,1270, 1272, 1274, and 1276 are formed.

It is to be noted that the electrodes and/or wirings 1268, 1270, 1272,1274, and 1276 may be formed of an aluminum alloy film that contains atleast one type of element of nickel (Ni), cobalt (Co), or iron (Fe) andcarbon (C), as well. With use of this kind of aluminum alloy film, thereis an advantage in that mutual diffusion of silicon and the materials ofwhich the electrodes or the like are formed can be prevented even if theelectrodes or the like make contact with silicon (Si). In addition, thiskind of aluminum alloy film has a characteristic such thatoxidation-reduction reactions do not occur even if this aluminum alloyfilm makes contact with a transparent conductive film, for example, atransparent conductive film formed using indium tin oxide (ITO), and thetwo films can be made to be in direct contact with each other.Furthermore, because this kind of aluminum alloy film has lowresistivity and excellent heat resistance, it is suitable for use as awiring material.

Moreover, for each of the electrodes and/or wirings 1268, 1270, 1272,1274, and 1276, a structure in which an electrode and a wiring areformed at the same time may be used, or a structure in which anelectrode and a wiring are formed separately and then connected togethermay be used, as well.

By the sequence of steps described above, a semiconductor substrate thatincludes a CMOS circuit 1284, which includes the n-channel TFT 1278 andthe p-channel TFT 1280, and the n-channel TFT 1282 can be formed (FIG.14C). It is to be noted that a fabrication method of a semiconductorsubstrate that can be used in the present invention is not limited tobeing the fabrication process described above. For example, a process bywhich a TFT is formed using an amorphous semiconductor film or a processby which a TFT is formed using a single-crystal semiconductor film maybe employed, as well. Furthermore, the TFTs are not limited to beingtop-gate TFTs, and bottom-gate TFTs may be used, as well.

Moreover, a semiconductor substrate that can be used in a liquid crystaldisplay device of the present invention is not limited to having astructure in which the driving circuit is formed over a singlesubstrate. For example, the driving circuit (or a part thereof) may beformed over a single-crystal substrate and that IC chip connected bychip-on-glass (COG) and placed over a glass substrate. In addition, theIC chip may be connected to a glass substrate using tape automatedbonding (TAB) or a printed circuit board.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 6, as appropriate.

Embodiment Mode 8

In the present embodiment mode, a fabrication process of a liquidcrystal display device will be described using FIG. 15, FIG. 16, andFIG. 17.

It is to be noted that the fabrication method of a liquid crystaldisplay device described in the present embodiment mode is a method inwhich a pixel section and a driver circuit section provided in theperiphery of the pixel section are fabricated together integrally. Forsake of simplicity, for the driver circuit, only a CMOS circuit, whichis a basic unit, is to be shown.

First, a semiconductor substrate is fabricated using methods and thelike given in Embodiment Mode 7. Here, in the present embodiment mode,an explanation will be given using the semiconductor substratefabricated using the method outlined in Embodiment Mode 7; however, thefabrication method of a liquid crystal display device of the presentinvention is not to be limited to this method.

First, the process up through formation of the electrodes and/or wirings1268, 1270, 1272, 1274, and 1276 is performed in accordance withEmbodiment Mode 7 (FIG. 14C). It is to be noted that in drawings usedhereinafter, the same reference numerals are used to denote componentsthat are the same as those of Embodiment Mode 7.

Next, a third interlayer insulating film 1500 is formed over the secondinterlayer insulating film 1266 and the electrodes and/or wirings 1268,1270, 1272, 1274, and 1276 (FIG. 15). It is to be noted that the thirdinterlayer insulating film 1500 can be formed using the same materialsas those used to form the second interlayer insulating film 1266.

Next, a resist mask is formed using a photo mask, and a part of thethird interlayer insulating film 1500 is removed by dry etching to forma contact hole. In formation of the contact hole, carbon tetrafluoride(CF₄), oxygen (O₂), and helium (He) at flow rates of 50 sccm, 50 sccm,and 30 sccm, respectively, are used as etching gases. It is to be notedthat the bottom of the contact hole reaches the electrode and/or wiring1276.

After the resist mask is removed, a fourth conductive film is formedover the entire surface. Next, the fourth conductive film is etched asselected, whereby a pixel electrode 1502 that is electrically connectedto the electrode and/or wiring 1276 is formed (FIG. 15). In cases inwhich a reflective liquid crystal display device is fabricated, thepixel electrode 1502 may be formed of a metal material of silver (Ag),gold (Au), copper (Cu), tungsten (W), aluminum (Al), or the like thatreflects light by a sputtering method. In cases in which a transmissiveliquid crystal display device is fabricated, the pixel electrode 1502can be formed using a transparent conductive film of indium tin oxide(ITO), indium tin oxide that contains silicon oxide, zinc oxide (ZnO),tin oxide (SnO₂), or the like.

It is to be noted that a dramatic effect may be obtained by use of thepresent invention in a transmissive liquid crystal display device;however, the present invention may be applied to a reflective liquidcrystal display device, as well. Furthermore, application of the presentinvention to a so-called transflective liquid crystal display device inwhich some of the pixels are of the reflective type and some of thepixels are of the transmissive type is effective, as well. Atransflective liquid crystal display device has advantages in thatluminance is easily secured and power consumption is easily reduced byuse thereof because the transflective liquid crystal display device canbe used as a reflective type when the amount of light from external ishigh and as a transmissive type when such is not the case.

An enlarged planar-view diagram of a part of the pixel section thatincludes the pixel TFT is shown in FIG. 16. In FIG. 16, to facilitateunderstanding of a condition of a lower section of the pixel electrode,the structure is given as one in which a pixel electrode of a pixel onthe right side of the diagram is omitted. It is to be noted that a crosssection of a line A-A′ in FIG. 16 corresponds to that of the line A-A′of the pixel section in FIG. 15, and the same reference numerals areused for parts in FIG. 16 that correspond to parts in FIG. 15.

As shown in FIG. 16, the gate electrode 1240 is connected to a gatewiring 1504. Moreover, the electrode and/or wiring 1274 is formedintegrated together with a source wiring. Furthermore, a capacitivewiring 1506 is formed, and a holding capacitor is formed from the firstinterlayer insulating film 1264, the pixel electrode 1502, and thecapacitive wiring 1506.

By the process given above, a pixel TFT that is formed of the top-gate,n-channel TFT 1282; the CMOS circuit 1284 that is formed of thetop-gate, n-channel TFT 1278 and the top-gate, p-channel TFT 1280; andthe pixel electrode 1502 are formed over the substrate 1200. In thepresent embodiment mode, an example in which top-gate TFTs are formed isgiven; however, bottom-gate TFTs may be formed, as well.

Next, an alignment film 1508 a is formed so as to cover the pixelelectrode 1502. It is to be noted that the alignment film 1508 a may beformed using a liquid droplet discharge method, a screen printingmethod, an offset printing method, or the like. After the alignment film1508 a is formed, rubbing treatment is performed on the surface of thealignment film 1508 a.

Next, a counter substrate 1510 that is to be attached to the substrate1200 is prepared. Here, on the counter substrate 1510, a color filterformed of a colored layer 1512 a, a light-blocking layer (black matrix)1512 b, and an overcoat layer 1514 is provided, and a counter electrode1516, further formed of a light-transmissive electrode or alight-reflective electrode, and an alignment film 1508 b are formed(FIG. 17). For the counter substrate 1510, a substrate that has aboutthe same size or the same shape as the substrate 1200 can be used. Here,there is no need for the about the same size and the same shape to beexactly the same, and the “about the same size” and “same shape” referto a size and shape that are more or less adequate in formation of apanel.

Next, the substrate 1200 and the counter substrate 1510 obtained by theaforementioned process are bonded together through a sealant. Here, aspacer may be provided between the alignment film 1508 a and thealignment film 1508 b in order that the gap between the two substratesbe maintained at an equal distance. Next, a liquid crystal 1518 isinjected into the space between the two substrates, and the twosubstrates are sealed using a sealing material. Thus, by provision ofpolarizing plates, a backlight, a light sensor, and the like, the liquidcrystal display device of the present invention is completed. It is tobe noted that the light sensor is provided in a location thatcorresponds to the monitor section. A pixel of the monitor section canbe fabricated in the same way as a pixel for display use. The monitorsection can be formed of one pixel or may be formed using two or morepixels. The area of the pixel of the monitor section may be the same asthe area of the pixel of the display section or larger than the area ofthe pixel of the display section. By the monitor section being formed ofa plurality of pixels, accuracy in detection of luminance can beimproved. Furthermore, by the area of the pixel of the monitor sectionbeing increased, accuracy in detection of luminance can be improvedsimilarly. In other words, fine control of the backlight can beperformed.

In addition, in a liquid crystal display device of the presentinvention, any one of methods such as a twisted nematic (TN) method, anin-plane switching (IPS) method, a fringe field switching (FFS) method,a multi-domain vertical alignment (MVA) method, a patterned verticalalignment (PVA) method, an axially symmetric aligned micro-cell (ASM)method, an optical compensated birefringence (OCB) method, aferroelectric liquid crystal (FLC) method, an anti-ferroelectric liquidcrystal (AFLC) method, or the like can be used.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 7, as appropriate.

Embodiment Mode 9

In the present embodiment mode, examples of fabrication methods of asemiconductor substrate that can be used in a display device of thepresent invention will be described using FIGS. 18A and 18B, FIGS. 19Aand 19B, FIGS. 20A and 20B, FIGS. 21A to 21C, FIGS. 22A to 22C, FIGS.23A to 23C, and FIGS. 24A and 24B. It is to be noted that thesemiconductor substrate of the present embodiment mode is a substratethat has a single-crystal semiconductor layer and an amorphoussemiconductor layer.

In FIGS. 18A and 18B, perspective-view diagrams of semiconductorsubstrates in which the present invention is used are shown.Furthermore, in FIGS. 19A and 19B and FIGS. 20A and 20B,cross-sectional-view diagrams of semiconductor substrates in which thepresent invention is used are shown.

In each of FIG. 18A and FIGS. 19A and 19B, a semiconductor substrate1800 has a structure in which a plurality of stacked-layer bodies, ineach of which an insulating layer 1820 and a single-crystalsemiconductor layer 1830 are stacked together in the order given, aswell as an insulating layer 1840 and an amorphous semiconductor layer1850 stacked together in the order given are provided over one surfaceof a base substrate 1810. Each of the single-crystal semiconductorlayers 1830 and the amorphous semiconductor layer 1850 are provided overthe base substrate 1810 with one of the insulating layers 1820interposed between each of the single-crystal semiconductor layers 1830and the base substrate 1810 and the insulating layer 1840 interposedbetween the amorphous semiconductor layer 1850 and the base substrate1810. That is, a plurality of the single-crystal semiconductor layers1830 is provided over a single base substrate 1810 and, furthermore, theamorphous semiconductor layer 1850 is provided, whereby a singlesemiconductor substrate 1800 is formed. It is to be noted that, in FIGS.18A and 18B, FIGS. 19A and 19B, and FIGS. 20A and 20B, for sake ofconvenience, only a structure of a case in which one panel is fabricatedfrom a single semiconductor substrate 1800; however, the presentinvention is not limited to having only this structure.

For the single-crystal semiconductor layer 1830, typically,single-crystal silicon is employed. In addition to single-crystalsilicon, a single-crystal semiconductor layer that is a compoundsemiconductor of silicon, germanium, gallium arsenide, indium phosphide,or the like that can be separated from a single-crystal semiconductorsubstrate using a hydrogen ion implantation separation method can beapplied, as well.

There are no particular limitations on the shape of the single-crystalsemiconductor layer 1830; however, setting the shape of thesingle-crystal semiconductor layer 1830 to be rectangular (including asquare shape) is preferable because processing is made easier and thesingle-crystal semiconductor layer 1830 can be attached to the basesubstrate 1810 with a favorable degree of integration if thesingle-crystal semiconductor layer 1830 is rectangular.

For the base substrate 1810, a substrate that has an insulating surfaceor an insulating substrate is used. Specifically, a glass substrate ofany of different types of glass used in the electronics industry, suchas aluminosilicate glass, aluminoborosilicate glass, barium borosilicateglass, or the like; a quartz substrate; a ceramic substrate; a sapphiresubstrate; or the like can used. Preferably, a glass substrate is used,and for example, a mother glass substrate with a large area referred toas sixth-generation (1500 mm×1850 mm), seventh-generation (1870 mm×2200mm), or eighth-generation (2200 mm×2400 mm) can be used. By use of amother glass substrate with a large area for the base substrate 1810, anincrease in the area of a semiconductor substrate can be realized. Inthe present embodiment mode, a case in which one panel is fabricatedfrom a single base substrate; in cases in which a plurality of panelsare fabricated from a single base substrate (cases with multiplepanels), the panels may be fabricated with adjustment of sizes of thesingle-crystal semiconductor layers 1830 and the amorphous semiconductorlayer 1850 as appropriate.

The insulating layers 1820 are each provided between the base substrate1810 and each of the single-crystal semiconductor layers 1830. Theinsulating layer 1820 may be set to have a single-layer structure or astacked-layer structure, and the surface (hereinafter referred to as abonding surface) of the insulating layer 1820 that comes into contactwith the base substrate 1810 is set to be a hydrophilic surface that issmooth.

In FIG. 19A, an example is shown in which a bonding layer 1822 is formedfor the insulating layer 1820. A silicon oxide layer is suitable for useas the bonding layer 1822 that can be formed of a hydrophilic surfacethat is smooth. In particular, use of a silicon oxide layer that isfabricated by a chemical vapor deposition method using an organic silaneis preferable. For the organic silane, an organic compound that containssilicon such as tetraethoxysilane (abbreviated designation: TEOS,chemical formula: Si(OC₂H₅)₄), tetramethylsilane (TMS, chemical formula:Si(CH₃)₄), trimethylsilane ((CH₃)₃SiH), tetramethylcyclotetrasiloxane(TMCTS), octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane(HMDS), triethoxysilane (SiH(OC₂H₅)₃), tris dimethyl aminosilane(SiH(N(CH₃)₂)₃), or the like can be used.

It is preferable that the bonding layer 1822 that is formed of ahydrophilic surface that is smooth be formed at a film thickness ofgreater than or equal to 5 nm and less than or equal to 500 nm. By thefilm thickness of the bonding layer 1822 being set to be within therange given, along with surface roughness of a surface that is to beformed being planarized, smoothness of the surface of the film that isgrowing can be secured. In addition, the amount of distortion within asubstrate (in FIG. 19A, the base substrate 1810) to which the film is tobe bonded can be reduced. It is to be noted that a silicon oxide layersuch as that of the bonding layer 1822 may be provided for the basesubstrate 1810, as well. In bonding of the single-crystal semiconductorlayer 1830 to the base substrate 1810, which is a substrate that has aninsulating surface or is an insulating substrate, by provision of abonding layer that is preferably made up of a silicon oxide layer formedusing an organic silane as a source material over one or both of thesurfaces that are to be bonded together, a strong bond can be formed.

In FIG. 19B, an example in which the insulating layer 1820 is set tohave a stacked-layer structure is shown. Specifically, an example isshown in which the insulating layer 1820 is formed of a stacked-layerstructure of the bonding layer 1822 and an insulating layer 1824 thatcontains nitrogen. It is to be noted that, because the bonding layer1822 is set so as to be formed over the surface to which the basesubstrate 1810 is to be bonded, the structure is set to be one in whichthe insulating layer 1824 that contains nitrogen is provided between thesingle-crystal semiconductor layer 1830 and the bonding layer 1822. Theinsulating layer 1824 that contains nitrogen is formed of a single-layerstructure or stacked-layer structure using any of a silicon nitridelayer, a silicon nitride oxide layer (SiN_(x)O_(y), where x>y), and asilicon oxynitride layer (SiO_(x)N_(y), where x>y). For example, asilicon oxynitride layer and a silicon nitride oxide layer can bestacked together from the single-crystal semiconductor layer 1830 sideand set to be the insulating layer 1824 that contains nitrogen.

It is to be noted that the insulating layer 1840 that is provided on thelower part of the amorphous semiconductor layer 1850 is not to be takenas being limited to having the same structure as the insulating layer1820 that is provided on the lower part of the single-crystalsemiconductor layer 1830; however, as shown in FIGS. 19A and 19B, it ispreferable that the material that makes contact with the amorphoussemiconductor layer 1850 and the material that makes contact with thesingle-crystal semiconductor layer 1830 at least be set to be the samematerial. By the materials that make contact with each of the amorphoussemiconductor layer 1850 and the single-crystal semiconductor layer 1830being set to be the same, etching characteristics in patterning that isto be formed during a subsequent step can be matched up.

It is to be noted that “silicon oxynitride layer” refers to a layer inwhich, in the composition, the amount of oxygen contained therein isgreater than the amount of nitrogen and, for example, oxygen iscontained at greater than or equal to 50 at. % and less than or equal to70 at. %; nitrogen, at greater than or equal to 0.5 at. % and less thanor equal to 15 at. %; silicon, at greater than or equal to 25 at. % andless than or equal to 35 at. %; and hydrogen, at greater than or equalto 0.1 at. % and less than or equal to 10 at. %. Furthermore, “siliconnitride oxide layer” refers to a layer in which, in the composition, theamount of nitrogen contained therein is greater than the amount ofoxygen and, for example, oxygen is contained at greater than or equal to5 at. % and less than or equal to 30 at. %; nitrogen, at greater than orequal to 20 at. % and less than or equal to 55 at. %; silicon, atgreater than or equal to 25 at. % and less than or equal to 35 at. %;and hydrogen, at greater than or equal to 10 at. % and less than orequal to 25 at. %. The aforementioned ranges are ranges for casesmeasured using Rutherford backscattering spectrometry (RBS) and hydrogenforward scattering (HFS). Moreover, the total for the content ratio ofthe constituent elements is taken to be a value that does not exceed 100at. %.

FIG. 18B and FIGS. 20A and 20B show examples in which an insulatinglayer 1860 that includes a bonding layer is formed over the basesubstrate 1810. The insulating layer 1860 may be formed as asingle-layer structure or a stacked-layer structure, and the surface ofthe insulating layer 1860 that comes into contact with thesingle-crystal semiconductor layer 1830 is formed so as to be ahydrophilic surface that is smooth. It is to be noted that it ispreferable that a barrier layer used to prevent the diffusion of mobileions of an alkali metal, alkaline earth metal, or the like from a glasssubstrate that is used as the base substrate 1810 be provided betweenthe base substrate 1810 and the bonding layer.

In FIG. 20A, an example is shown in which a stacked-layer structure ofthe barrier layer 1862 and a bonding layer 1864 is formed for theinsulating layer 1860. For the bonding layer 1864, the same kind ofsilicon oxide layer as for the bonding layer 1822 may be provided.Alternatively, a bonding layer appropriate to the single-crystalsemiconductor layer 1830 may be provided, as well. In FIG. 20A, anexample is shown in which the bonding layer 1822 is provided over thesingle-crystal semiconductor layer 1830 as well. By the structure beingset to be this kind of structure, because a bond is formed by bondinglayer to bonding layer in bonding of the base substrate 1810 and thesingle-crystal semiconductor layer 1830, an even stronger bond can beformed. The barrier layer 1862 is formed as a single-layer structure orstacked-layer structure using any of a silicon oxide layer, a siliconnitride layer, a silicon oxynitride layer, and a silicon nitride oxidelayer. Preferably, the barrier layer 1862 is formed using an insulatinglayer that contains nitrogen.

In FIG. 20B, an example is shown in which a bonding layer is providedover the base substrate 1810. Specifically, a stacked-layer structure ofthe barrier layer 1862 and the bonding layer 1864 are provided over thebase substrate 1810 as the insulating layer 1860. Furthermore, a siliconoxide layer 1826 is provided over the single-crystal semiconductor layer1830. In bonding of the single-crystal semiconductor layer 1830 to thebase substrate 1810, the silicon oxide layer 1826 forms a bond with thebonding layer 1864. It is preferable that the silicon oxide layer 1826be formed by a thermal oxidation method. Furthermore, a chemical oxidecan also be applied for the silicon oxide layer 1826. A chemical oxidecan be formed, for example, by treatment of a surface of asingle-crystal substrate with water that contains ozone. Use of achemical oxide is favorable because chemical oxides are formedreflecting the planarity of the surface of the single-crystal substrate.

It is to be noted that the insulating layer 1840 that is provided on thelower part of the amorphous semiconductor layer 1850 is not to be takenas being limited to having the same structure as the bonding layer 1822and the silicon oxide layer 1826 that are provided on the lower part ofthe single-crystal semiconductor layer 1830; however, as shown in FIGS.19A and 19B, it is preferable that the material that makes contact withthe amorphous semiconductor layer 1850 and the material that makescontact with the single-crystal semiconductor layer 1830 at least be setto be the same material. By the materials that make contact with each ofthe amorphous semiconductor layer 1850 and the single-crystalsemiconductor layer 1830 being set to be the same, etchingcharacteristics in patterning that is to be formed during a subsequentstep can be matched up.

Next, a fabrication method of a semiconductor substrate will bedescribed. Here, an example of the fabrication method of a semiconductorsubstrate that is shown in FIG. 19B will be described using FIGS. 21A to21C, FIGS. 22A to 22C, FIGS. 23A to 23C, and FIGS. 24A and 24B. It is tobe noted that, needless to say, structures shown in FIG. 19A, FIGS. 20Aand 20B, and the like can be fabricated in the same way.

First, as shown in FIG. 21A, an insulating layer 2102 is formed over abase substrate 2100. For the base substrate 2100, for example, any ofthe substrates described above can be used. Furthermore, a flexiblesubstrate formed of a synthetic resin such as a plastic typified by PET,PES, or PEN; acrylic; or the like can also be used.

The insulating layer 2102 is provided to prevent an alkali metal, suchas Na or the like, or an alkaline earth metal contained within the basesubstrate 2100 from diffusing into a semiconductor film and impartingadverse effects on the characteristics of a semiconductor element.Consequently, the insulating layer 2102 is formed using an insulatingmaterial of silicon nitride or silicon oxide that contains nitrogen bywhich the diffusion of an alkali metal or alkaline earth metal into asemiconductor film can be suppressed. In the present embodiment mode, asilicon oxide film that contains nitrogen is formed for the insulatinglayer 2102 so as to have a film thickness greater than or equal to 10 nmand less than or equal to 400 nm (preferably, greater than or equal to50 nm and less than or equal to 300 nm) using a plasma CVD method.

Next, a semiconductor layer 2104 is formed over the insulating layer2102. The film thickness of the semiconductor layer 2104 is set to begreater than or equal to 25 nm and less than or equal to 100 nm(preferably, greater than or equal to 30 nm and less than or equal to 60nm). It is to be noted that the semiconductor layer 2104 may be formedof an amorphous semiconductor or a polycrystalline semiconductor. Inaddition, for the semiconductor, not only silicon (Si) but also silicongermanium (SiGe) or the like can be used. When silicon germanium isused, it is preferable that the concentration of germanium be greaterthan or equal to 0.01 at. % approximately and less than or equal to 4.5at. % approximately.

Next, as shown in FIG. 21B, crystallization is performed by irradiationof the semiconductor layer 2104 with a linear laser beam 2108. If lasercrystallization is performed as in the present embodiment mode, in orderto increase the tolerance of the semiconductor layer 2104 to a laserbeam, a heat treatment step performed at a temperature of 500° C. forone hour may be added before the laser crystallization step.

In the laser crystallization step, for example, a continuous wave laser(a CW laser), a quasi-continuous wave laser (a pulsed laser with arepetition rate of 10 MHz or more, preferably, 80 MHz or more), or thelike can be used.

Specifically, for a continuous wave laser, an Ar laser, a Kr laser, aCO₂ laser, a YAG laser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, aGdVO₄ laser, a Y₂O₃ laser, a ruby laser, an alexandrite laser, aTi:sapphire laser, a helium-cadmium laser, and the like can be given.

Furthermore, for a quasi-CW laser, a pulsed laser such as an Ar laser, aKr laser, an excimer laser, a CO₂ laser, a YAG laser, a YVO₄ laser, aYLF laser, a YAlO₃ laser, a GdVO₄ laser, a Y₂O₃ laser, a ruby laser, analexandrite laser, a Ti:sapphire laser, a copper vapor laser, or a goldvapor laser can be given.

This kind of pulsed laser comes to exhibit the same effects as acontinuous wave laser if the repetition rate is increased.

For example, when a solid-state laser capable of continuous oscillationis used, by irradiation at the second through fourth harmonics of afundamental frequency, crystals with a large grain size can be obtained.Typically, the second harmonic (532 nm) or third harmonic (355 nm) of aYAG laser (a fundamental of 1064 nm) can be used. The power density maybe set to be greater than or equal to 0.01 MW/cm² and less than or equalto 100 MW/cm² (preferably, greater than or equal to 0.1 MW/cm² and lessthan or equal to 10 MW/cm²).

As described above, by irradiation of the semiconductor layer 2104 witha laser beam, a crystalline semiconductor layer 2110 with even highercrystallinity is formed.

It is to be noted that, in the present embodiment mode, an example isgiven in which the crystalline semiconductor layer 2110 is formed usingirradiation with laser light; however, the present invention is notlimited to having this configuration only. In order to simplify aprocess, the semiconductor layer 2104 may be used without performance ofa crystallization process, as well.

Next, as shown in FIG. 21C, the crystalline semiconductor layer 2110 isetched as selected, and the insulating layer 2102 is further etched sothat a part of the surface of the base substrate is exposed. Duringetching of the crystalline semiconductor layer 2110, island-shapedsemiconductor layers that are to form a pixel TFT during a subsequentstep may be formed, as well. By the steps described above, thecrystalline semiconductor layer (amorphous semiconductor layer) 2110 isformed over the base substrate 2100.

Next, a single-crystal semiconductor layer is formed. First, asingle-crystal substrate 2200 is prepared (with reference to FIG. 22Aand FIG. 23A). For the single-crystal substrate 2200, a commerciallyavailable semiconductor substrate may be used, and for example, asilicon substrate; a germanium substrate; a compound semiconductorsubstrate of gallium arsenide, indium phosphide, or the like; and thelike can be given. For a commercially available silicon substrate, asubstrate with a size of a diameter of 5 inches (125 millimeters), adiameter of 6 inches (150 millimeters), a diameter of 8 inches (200millimeters), or a diameter of 12 inches (300 millimeters) is typical,and the shape of the substrate is often round. In addition, a filmthickness of up to approximately 1.5 mm can be selected as appropriate.

Next, ions 2202 accelerated by an electric field are introduced into thesingle-crystal substrate 2200 at a given depth from the surface of thesingle-crystal substrate 2200, whereby an ion doping layer 2204 (canalso be referred to as a damaged region) is formed (with reference toFIG. 22A and FIG. 23A). Implantation of the ions 2202 is performed inconsideration of the film thickness of a single-crystal semiconductorlayer that is to be transferred to a base substrate during a subsequentstep. Preferably, the film thickness of the single-crystal semiconductorlayer is set so as to be a thickness of from 5 nm to 500 nm, morepreferably, a thickness of from 10 nm to 200 nm.

For the ions 2202, ions of hydrogen, helium, or a halogen such asfluorine or the like can be used. It is to be noted that, for the ions2202, use of ion species of a single type of atom or made from aplurality of the same type of atom generated by plasma excitation of asource gas selected from hydrogen, helium, or a halogen element ispreferable. Cases of implantation of hydrogen ions are preferablebecause, along with H⁺, H₂ ⁺, and H₃ ⁺ ions being included, if theproportion of the number of H₃ ⁺ ions is increased, implantationefficiency of ions can be increased and the length of time forimplantation can be shortened. Furthermore, by the structure being setto be this kind of structure, separation of substrates can be performedeasily.

It is to be noted that, in order to form the ion doping layer 2204 atthe given depth, there are cases in which implantation of the ions 2202under conditions of high dosing becomes necessary. In these cases, thesurface of the single-crystal substrate 2200 may be roughened dependingon the conditions. For this reason, a silicon nitride layer, a siliconnitride oxide layer, or the like may be provided at a film thicknesswithin the range of from 50 nm to 200 nm over the surface of thesingle-crystal semiconductor substrate into which the ions are to beimplanted as a protective layer.

Next, after the insulating layer 2206 is formed over the single-crystalsubstrate 2200, the bonding layer 2208 is formed (with reference to FIG.22B and FIG. 23B). Next, after the insulating layer 2206 is formed overthe single-crystal substrate 2200, the bonding layer 2208 is formed(with reference to FIG. 22B and FIG. 23B). It is preferable that theinsulating layer 2206 be formed of the same materials as the insulatinglayer 2102 although the present invention not limited thereto.

For the insulating layer 2206 of the present embodiment mode, a siliconoxide film that contains nitrogen is formed using a plasma CVD method.The bonding layer 2208 is formed over a surface at which thesingle-crystal substrate 2200 forms a bond with the base substrate. Forthe bonding layer 2208 formed here, use of a silicon oxide layer formedby film formation by a chemical vapor deposition method using an organicsilane as a source gas as described above is preferable. In addition, asilicon oxide layer formed by film formation by a chemical vapordeposition method in which a silane is used as a source gas can beapplied, as well. In the film formation by a chemical vapor depositionmethod, temperatures of a degree at which degassing from the ion dopinglayer 2204 formed over the single-crystal substrate 2200 does not occurare applied. For example, a film formation temperature of 350° C. orless is applied. It is to be noted that, for thermal treatment inseparation of the single-crystal semiconductor layer from thesingle-crystal substrate, a thermal treatment temperature that is higherthan the film formation temperature in a chemical vapor depositionmethod is applied.

Next, the single-crystal substrate 2200 is processed into a desired sizeand shape (with reference to FIG. 22C and FIG. 23C). In FIG. 23C, anexample is shown in which a round single-crystal substrate 2200 isdivided up and rectangular single-crystal substrates 2210 are formed. Inthis case, the insulating layer 2206, the bonding layer 2208, and theion doping layer 2204 are also divided up. That is, the single-crystalsubstrates 2210 that each have a desired size and shape, in each ofwhich is formed the ion doping layer 2204 at a given depth and over asurface (the surface that is to be bonded to the base substrate) of eachof which is formed the bonding layer 2208, are obtained.

Although the size of the single-crystal substrate 2210 can be set to beequal to a desired size, here, the size of the single-crystal substrate2210 is set to be equal to the size of the driver circuit. The size ofthe driver circuit may be selected as appropriate based on the areaneeded for the driver circuit. Having the shape of the single-crystalsubstrate 2210 be set to be rectangular is preferable because processingduring a subsequent fabrication step comes to be performed more easilyand, furthermore, the single-crystal substrate 2210 can be cut out fromthe single-crystal substrate 2200 more efficiently, as well. Division ofthe single-crystal substrate 2200 can be performed using a cuttingapparatus such as a dicer, a wire saw, or the like or by laser cutting,plasma cutting, or electron beam cutting or any other given cuttingmeans.

It is to be noted that the order of steps up through the step forformation of a bonding layer over a surface of a single-crystalsubstrate can be switched around as appropriate. In FIGS. 22A to 22C andFIGS. 23A to 23C, an example is shown in which, after an ion dopinglayer is formed in a single-crystal substrate and an insulating layerand a bonding layer are formed over a surface of the single-crystalsubstrate, the single-crystal substrate is processed into a desiredpanel size. However, another process can be used, for example, a processin which, after a single-crystal substrate is processed into a desiredpanel size, an ion doping layer is formed in the single-crystalsubstrate that has been processed into a desired panel size and aninsulating layer and a bonding layer are formed over the surface of thesingle-crystal substrate of the desired panel size.

Next, the base substrate 2100 and the single-crystal substrate 2210 arebonded together. In FIG. 24A, an example is shown in which the basesubstrate 2100 and a surface formed by the bonding layer 2208 of thesingle-crystal substrate 2210 are placed in contact with each other, andthe base substrate 2100 and the bonding layer 2208 are bonded together,whereby the single-crystal substrate 2210 is attached to the basesubstrate 2100. It is to be noted that it is preferable that thesurfaces (bonding surfaces) over which the bond is to be formed besufficiently cleaned. By the base substrate 2100 and the bonding layer2208 being placed in contact with each other, a bond is formed. Van derWaals forces are acting in this bond, and by pressure being applied tothe base substrate 2100 and the single-crystal substrate 2210, a strongbond can be formed by hydrogen bonds.

In addition, in order to form a favorable bond between the basesubstrate 2100 and the bonding layer 2208, the bonding surfaces may beactivated. For example, one or both of the surfaces by which the bond isformed are irradiated with an atom beam or an ion beam. When an atombeam or an ion beam is used, a neutral atom beam of an inert gas ofargon or the like or an ion beam of an inert gas can be used. Inaddition, the bonding surfaces may be activated by performance of plasmairradiation or radical treatment. By this kind of surface treatment,formation of bonds between different kinds of materials even attemperatures of 400° C. or less becomes easy to perform.

Moreover, it is preferable that heat treatment or pressure treatment beperformed after the base substrate 2100 and the single-crystal substrate2210 are bonded together with the bonding layer 2208 interposedtherebetween. By performance of heat treatment or pressure treatment,bonding strength can be increased. It is preferable that the temperaturefor heat treatment be a temperature lower than or equal to the uppertemperature limit of the base substrate 2100. Pressure treatment isperformed such that pressure is applied in a direction perpendicular tothe bonding surfaces, in consideration of the resistance to pressure ofthe base substrate 2100 and the single-crystal substrate 2210.

Next, heat treatment is performed, and a part of the single-crystalsubstrate 2210 is separated from the base substrate 2100 using the iondoping layer 2204 as a cleavage plane (with reference to FIG. 24B). Itis preferable that heat treatment be performed at a temperature higherthan or equal to the temperature for film formation of the bonding layer2208 and lower than or equal to the upper temperature limit of the basesubstrate 2100. For example, by performance of heat treatment at atemperature of from 400° C. to 600° C., changes in the volume of minutecavities formed in the ion doping layer 2204 occur, and cleavage alongthe ion doping layer 2204 becomes possible. Because the bonding layer2208 is bonded to the base substrate 2100, the single-crystalsemiconductor layer 2212 that has the same crystallinity as thesingle-crystal substrate 2210 comes to be left remaining over the basesubstrate 2100.

By the above process, a single-crystal semiconductor substrate is formedin which the single-crystal semiconductor layer 2212 is provided overthe base substrate 2100 with the bonding layer 2208 interposedtherebetween and the crystalline semiconductor layer (an amorphoussemiconductor layer) 2110 is provided. It is to be noted that thesingle-crystal semiconductor substrate described in the presentembodiment mode is a structure in which a plurality of single-crystalsemiconductor substrates are provided over a single base substrate withbonding layers interposed between each of the single-crystalsemiconductor substrates and the base substrate; however, thesingle-crystal semiconductor substrate of the present invention is notlimited to having this structure.

It is to be noted that it is preferable that the surface of thesingle-crystal semiconductor layer obtained by separation be polished bychemical mechanical polishing (CMP) so as to be planarized. Moreover,the surface of the single-crystal semiconductor layer may be planarizedby irradiation of the surface with laser light without any use of aphysical polishing means such as CMP or the like. It is to be noted thatit is preferable that irradiation by laser light be performed under anitrogen atmosphere that contains oxygen at a concentration of 10 ppm orless. This is because the surface of the single-crystal semiconductorlayer may be made rough if irradiation by laser light is performed underan oxygen atmosphere. In addition, CMP or the like may be performed inorder to thin the obtained single-crystal semiconductor layer, as well.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 8, as appropriate.

Embodiment Mode 10

In the present embodiment mode, a fabrication method of a liquid crystaldisplay device of the present invention will be described using FIGS.25A to 25C, FIGS. 26A to 26D, FIGS. 27A to 27C, and FIGS. 28A to 28C. Itis to be noted that, in the present embodiment mode, an example offabrication of a liquid crystal display device in which thesemiconductor substrate fabricated in Embodiment Mode 9 is used isgiven.

FIG. 25A is a top-view schematic diagram of a liquid crystal displaydevice, FIG. 25B is a cross-sectional-view diagram taken along a line OPof FIG. 25A, and FIG. 25C is a perspective-view diagram of the liquidcrystal display device.

A liquid crystal display device of the present embodiment mode has adisplay section 2520, a first driver circuit section 2530, and a seconddriver circuit section 2550 provided over a first substrate 2500. Thedisplay section 2520, the first driver circuit section 2530, and thesecond driver circuit section 2550 are sealed in between the firstsubstrate 2500 and a second substrate 2590 by a sealant 2580.Furthermore, a terminal region 2570 that is connected to an externalinput terminal that transmits a signal from external to the first drivercircuit section 2530 and the second driver circuit section 2550 isprovided over the first substrate 2500.

As shown in FIG. 25B, a pixel circuit section 2522 that has a transistoris provided in the display section 2520. Furthermore, a peripheralcircuit section 2532 that has a transistor is provided in the firstdriver circuit section 2530. An insulating layer 2502 is providedbetween the first substrate 2500 and the pixel circuit section 2522. Abonding layer 2504 and an insulating layer 2506 are stacked togetherbetween the first substrate 2500 and the peripheral circuit section2532. It is to be noted that the structure may be set to be one in whichan insulating layer that functions as a base insulating layer isprovided over the substrate 2500. In the pixel circuit section 2522 andperipheral circuit section 2532 or as upper layers thereover, aninsulating layer 2508 and an insulating layer 2509 that each function asan interlayer insulating layer are provided. A source electrode or drainelectrode of the transistor formed in the pixel circuit section 2522 iselectrically connected to a pixel electrode 2560 through an openingformed in the insulating layer 2509. It is to be noted that a circuit inwhich transistors are used is integrated into the pixel circuit section2522; however, here, for sake of simplicity, a cross-sectional-viewdiagram of only one transistor is shown. In the same way, a circuit inwhich transistors are used is integrated into the peripheral circuitsection 2532; however, for sake of simplicity, a cross-sectional-viewdiagram of only two transistors is shown.

Over the pixel circuit section 2522 and peripheral circuit section 2532,a liquid crystal layer 2584 that is interposed between an alignment film2582, which is formed so as to cover the pixel electrode 2560, and analignment film 2587 is provided. For the liquid crystal layer 2584, thedistance (cell gap) is controlled by a spacer 2586. Over the alignmentfilm 2587, a second substrate 2590 is provided with a counter electrode2588 and a color filter 2589 interposed between the alignment film 2587and the second substrate 2590. The first substrate 2500 and the secondsubstrate 2590 are fixed in place by the sealant 2580.

Moreover, a polarizing plate 2591 is placed over the outer side of thefirst substrate 2500, and a polarizing plate 2592 is placed over theouter side of the second substrate 2590. It is to be noted that thepresent invention can be applied to any of a transmissive type, areflective type, or transflective type, which is a combination of atransmissive type and a reflective type, of liquid crystal displaydevice; however, out of these types, the effect is particularlyprominent for cases in which the present invention is used in atransmissive type or transflective type of liquid crystal displaydevice.

Furthermore, a terminal electrode 2574 is provided in the terminalregion 2570. The terminal electrode 2574 is electrically connected to anexternal input terminal 2578 through an anisotropic conductive layer2576.

Next, an example of a fabrication method of the liquid crystal displaydevice shown in FIGS. 25A to 25C will be described.

First, a semiconductor substrate is prepared (with reference to FIG.26A). Here, an example is shown in which a semiconductor substratesimilar to the one shown in FIG. 19B is applied; however, the presentinvention is not limited thereto.

Over the substrate 2500, which is a base substrate, an amorphoussemiconductor layer 2510 is provided with the insulating layer 2502interposed between the substrate 2500 and the semiconductor layer 2510,and a plurality of single-crystal semiconductor layers 2511 are providedwith the bonding layer 2504 and the insulating layer 2506 providedbetween the substrate 2500 and each of the plurality of single-crystalsemiconductor layers 2511. For the substrate 2500, a substrate that hasan insulating surface or an insulating substrate is used. For example, aglass substrate of any of different types of glass used in theelectronics industry, such as aluminosilicate glass, aluminoborosilicateglass, barium borosilicate glass, and the like, a quartz substrate; aceramic substrate; a sapphire substrate, or the like can be used. Here,a glass substrate is set to be used.

It is to be noted that in order to prevent the diffusion of mobile ionsof an alkali metal, an alkaline earth metal, and the like from a glasssubstrate, an insulating layer that functions as a base insulating layermay be provided separately. Specifically, it is preferable that aninsulating layer that contains nitrogen, such as a silicon nitridelayer, a silicon nitride oxide layer, or the like, be provided.

Next, the amorphous semiconductor layer 2510 is etched so that anamorphous semiconductor layer 2521 is formed in the display section2520, and the single-crystal semiconductor layers 2511 are etched sothat a first single-crystal semiconductor layer 2531 and a secondsingle-crystal semiconductor layer 2541 are formed in the first drivercircuit section 2530. Then, gate electrodes 2514 are formed over theamorphous semiconductor layer 2521, the first single-crystalsemiconductor layer 2531, and the second single-crystal semiconductorlayer 2541 with a gate insulating layer 2512 interposed between the gateelectrodes 2514 and each of the amorphous semiconductor layer 2521, thefirst single-crystal semiconductor layer 2531, and the secondsingle-crystal semiconductor layer 2541 (with reference to FIG. 26B).

It is to be noted that, in order to control threshold voltage of acompleted transistor, an impurity element imparting one type ofconductivity at low concentration may be added to the amorphoussemiconductor layer 2521, the first single-crystal semiconductor layer2531, and the second single-crystal semiconductor layer 2541. In thiscase, the impurity element is also added to the channel formation regionof the transistor, as well. It is to be noted that the impurity elementthat is added here is added at a lower concentration than theconcentration of a high-concentration impurity region that functions asa source region or a drain region and a low-concentration impurityregion that functions as a LDD region.

For the gate electrodes 2514, after a conductive layer is formed overthe entire surface of the substrate, the conductive layer is etched asselected and processed into desired shapes. Here, after a stacked-layerstructure of the conductive layer is formed for the gate electrodes2514, the conductive layer is etched as selected, and the separatedconductive layers are processed so as to cross over each of theamorphous semiconductor layer 2521, the first single-crystalsemiconductor layer 2531, and the second single-crystal semiconductorlayer 2541.

The conductive layers forming the gate electrodes 2514 can be formedsuch that, after a conductive layer is formed over the entire surface ofthe substrate using a metal element such as tantalum (Ta), tungsten (W),titanium (Ti), molybdenum (Mo), chromium (Cr), aluminum (Al), copper(Cu), niobium (Nb), or the like or an alloy material or a compoundmaterial containing one or more of these metal elements by a CVD methodor a sputtering method, the conductive layer is etched as selected toform the conductive layers forming the gate electrodes 2514. Inaddition, the conductive layers forming the gate electrodes 2514 can beformed using a semiconductor material typified by polycrystallinesilicon to which is added an impurity element such as phosphorus or thelike that imparts one type of conductivity.

It is to be noted that, here, an example is shown in which the gateelectrodes 2514 are each formed of a stacked-layer structure ofconductive layers of two layers; however, the gate electrodes may eachhave a single-layer structure or a stacked-layer structure of three ormore layers. In addition, side surfaces of the conductive layers may beset to each have a tapered shape. When the gate electrode is set to havea stacked-layer structure of conductive layers, the width of the bottomlayer of the conductive layers may be increased and side surfaces ofeach layer may be set to have a taper shape of differing angles oftaper.

The gate insulating layers 2512 are formed using a material such assilicon oxide, silicon oxynitride, hafnium oxide, aluminum oxide,tantalum oxide, or the like using a CVD method, a sputtering method, anALD method, or the like. Furthermore, the gate insulating layers 2512can be formed by solid-state oxidation or solid-state nitridation of theamorphous semiconductor layer 2521, the first single-crystalsemiconductor layer 2531, and the second single-crystal semiconductorlayer 2541 by plasma treatment. Alternatively, the gate insulatinglayers 2512 may be formed such that, after an insulating layer is formedby a CVD method or the like, the insulating layer is oxidized bysolid-state oxidation or nitrided by solid-state nitridation to form thegate insulating layers 2512.

It is to be noted that, in FIG. 26B, an example is shown in which sideedges of each of the gate insulating layers 2512 and each of the gateelectrodes 2514 are processed so as to match up; however, there are noparticular limitations on the structures of the gate insulating layers2512 and the gate electrodes 2514, and the gate insulating layers 2512may be processed so as to be left remaining during etching of the gateelectrodes 2514.

Furthermore, when a substance with a high dielectric constant (asubstance referred to as a “high-k material”) is used in the gateinsulating layers 2512, the gate electrodes 2514 are formed ofpolycrystalline silicon, a silicide, a metal, or a metal nitride.Preferably, the gate electrodes 2514 are formed of a metal or a metalnitride. For example, out of the conductive layers forming each of thegate electrodes 2514, the conductive layer that makes contact with thegate insulating layer 2512 is formed of a metal nitride material andupper conductive layers thereof are formed of a metal material. By useof this kind of combination, the widening of a depletion layer formed inthe gate electrode can be prevented even when the gate insulating layeris made to be thin, and reduction of driving performance of thetransistor can be prevented even when the transistor is miniaturized.

Next, an insulating layer 2516 is formed over the gate electrodes 2514.Then, an impurity element imparting one type of conductivity is addedusing the gate electrodes 2514 as masks (with reference to FIG. 26C).Here, an example is shown in which impurity elements impartingconductivity of different types are added to the first single-crystalsemiconductor layer 2531 and the second single-crystal semiconductorlayer 2541 that are formed in the first driver circuit section 2530.Furthermore, an example is shown in which an impurity element impartingthe same type of conductivity as the impurity element added to the firstsingle-crystal semiconductor layer 2531 is added to the amorphoussemiconductor layer 2521 that is formed in the display section 2520.

In the amorphous semiconductor layer 2521 that is formed in the displaysection 2520, a pair of impurity regions 2523 and a channel formationregion 2525 placed between the pair of impurity regions 2523 are formedin a self-aligning manner using the gate electrode 2514 as a mask.

In the first single-crystal semiconductor layer 2531 that is formed inthe first driver circuit section 2530, a pair of impurity regions 2533and a channel formation region 2535 placed between the pair of impurityregions 2533 are formed in a self-aligning manner using the gateelectrode 2514 as a mask. In the second single-crystal semiconductorlayer 2541, a pair of impurity regions 2543 and a channel formationregion 2545 placed between the pair of impurity regions 2543 are formedin a self-aligning manner using the gate electrode 2514 as a mask.Impurity elements imparting conductivity of different types are added tothe impurity regions 2533 and the impurity regions 2543.

For an impurity element imparting one type of conductivity, an elementimparting p-type conductivity such as boron (B), aluminum (Al), gallium(Ga), or the like or an element imparting n-type conductivity such asphosphorus (P), arsenic (As), or the like can be used. In the presentembodiment mode, an element, for example, phosphorus, imparting n-typeconductivity is added to the amorphous semiconductor layer 2521 formedin the display section 2520 and to the first single-crystalsemiconductor layer 2531 formed in the first driver circuit section2530. Moreover, an element, for example, boron, imparting p-typeconductivity is added to the second single-crystal semiconductor layer2541. It is to be noted that, in addition of the impurity element to theamorphous semiconductor layer 2521 and the first single-crystalsemiconductor layer 2531, the second single-crystal semiconductor layer2541 may be covered as selected using a resist mask or the like.Similarly, in addition of the impurity element to the secondsingle-crystal semiconductor layer 2541, the amorphous semiconductorlayer 2521 and the first single-crystal semiconductor layer 2531 may becovered as selected using a resist mask or the like.

The insulating layer 2516 can be formed using a material such as siliconoxide, silicon oxynitride, silicon nitride, silicon nitride oxide, orthe like using a CVD method, a sputtering method, an ALD method, or thelike. In the addition of the impurity element that imparts one type ofconductivity, by the configuration being set to be one in which theimpurity element that imparts one type of conductivity is added by beingpassed through the insulating layer 2516, the amount of damage for theamorphous semiconductor layer and the single-crystal semiconductor layercan be reduced.

Next, sidewall insulating layers 2518 are formed on side surfaces of thegate electrodes 2514. Then, the impurity element imparting one type ofconductivity is added using the gate electrodes 2514 and the sidewallinsulating layers 2518 as masks (with reference to FIG. 26D). It is tobe noted that impurity elements of the same conductivities as those ofthe impurity elements added to the amorphous semiconductor layer 2521,the first single-crystal semiconductor layer 2531, and the secondsingle-crystal semiconductor layer 2541 during respective precedingsteps (steps in which the impurity region 2523, the impurity region2533, and the impurity region 2543 are formed). Furthermore, theimpurity elements are added at concentrations higher than those of theimpurity elements added during the preceding steps.

In the amorphous semiconductor layer 2521, a pair of high-concentrationimpurity regions 2526 and a pair of low-concentration impurity regions2524 are formed in a self-aligning manner using the gate electrode 2514and the sidewall insulating layer 2518 as masks. Here, each of thehigh-concentration impurity regions 2526 that are formed functions as asource region or a drain region and the low-concentration impurityregions 2524 that are formed function as lightly doped drain (LDD)regions.

In the first single-crystal semiconductor layer 2531, a pair ofhigh-concentration impurity regions 2536 and a pair of low-concentrationimpurity regions 2534 are formed in a self-aligning manner using thegate electrode 2514 and the sidewall insulating layer 2518 as masks.Here, each of the high-concentration impurity regions 2536 that areformed functions as a source region or a drain region and thelow-concentration impurity regions 2534 that are formed function aslightly doped drain (LDD) regions. In the second single-crystalsemiconductor layer 2541, a pair of high-concentration impurity regions2546 and a pair of low-concentration impurity regions 2544 are formed ina self-aligning manner using the gate electrode 2514 and the sidewallinsulating layer 2518 as masks.

It is to be noted that, in addition of the impurity element to theamorphous semiconductor layer 2521 and the first single-crystalsemiconductor layer 2531, the second single-crystal semiconductor layer2541 may be covered as selected using a resist mask or the like.Similarly, in addition of the impurity element to the secondsingle-crystal semiconductor layer 2541, the amorphous semiconductorlayer 2521 and the first single-crystal semiconductor layer 2531 may becovered as selected using a resist mask or the like.

The sidewall insulating layers 2518 are provided on side surfaces of thegate electrodes 2514 with the insulating layer 2516 interposed betweenthe sidewall insulating layers 2518 and the gate electrodes 2514. Forexample, by performance of anisotropic etching in a perpendiculardirection of an insulating layer that is formed so that each of the gateelectrodes 2514 is buried, the sidewall insulating layers 2518 can beformed on side surfaces of the gate electrodes 2514 in a self-aligningmanner. The sidewall insulating layers 2518 can be formed using amaterial such as silicon nitride, silicon nitride oxide, silicon oxide,silicon oxynitride, or the like. It is to be noted that when theinsulating layer 2516 is formed using silicon oxide or siliconoxynitride, the insulating layer 2516 can be made to function as anetching stopper if the sidewall insulating layers 2518 are formed usingsilicon nitride or silicon nitride oxide. In addition, when theinsulating layer 2516 is formed using silicon nitride or silicon nitrideoxide, the sidewall insulating layers 2518 may be formed using siliconoxide or silicon oxynitride. In this way, by provision of an insulatinglayer that can function as an etching stopper, etching of the amorphoussemiconductor layer and the single-crystal semiconductor layer due tooveretching in formation of the sidewall insulating layers can beprevented.

Next, exposed portions of the insulating layer 2516 are etched to forman insulating layer 2517 (with reference to FIG. 27A). The insulatinglayer 2517 is left remaining between the sidewall insulating layers 2518and the gate electrodes 2514, between the sidewall insulating layers2518 and the amorphous semiconductor layer 2521, between the sidewallinsulating layers 2518 and the first single-crystal semiconductor layer2531, and between the sidewall insulating layers 2518 and the secondsingle-crystal semiconductor layer 2541.

It is to be noted that a silicide layer may be formed in order to lowerthe resistance of each of the high-concentration impurity regions thateach function as a source region or drain region. For the silicidelayer, a cobalt silicide or a nickel silicide may be applied. When thefilm thickness of the amorphous semiconductor layer and thesingle-crystal semiconductor layer is thin, a silicide reaction may bemade to proceed to the bottom portion of the amorphous semiconductorlayer and the single-crystal semiconductor layer in which thehigh-concentration impurity regions are formed so that the amorphoussemiconductor layer and the single-crystal semiconductor layer in whichthe high-concentration impurity regions are formed are fully silicided.

Next, after the insulating layer 2508 is formed over the entire surfaceof the substrate 2500, the insulating layer 2508 is etched as selected,and openings that each reach one of the high-concentration impurityregions 2526 that are formed in the amorphous semiconductor layer 2521of the display section 2520 are formed. Furthermore, openings that eachreach one of the high-concentration impurity regions 2536 or one of thehigh-concentration impurity regions 2546 that are formed in the firstsingle-crystal semiconductor layer 2531 and the second single-crystalsemiconductor layer 2541, respectively, of the first driver circuitsection 2530 are formed. Then, conductive layers 2519 are formed so thateach of the openings is buried. Moreover, a terminal electrode 2574 isformed in the terminal region 2570 (with reference to FIG. 27B).

The insulating layer 2508 is formed by a CVD method, a sputteringmethod, an ALD method, a coating method, or the like using an inorganicinsulating material that contains oxygen or nitrogen such as siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide, orthe like; an insulating material that contains carbon such asdiamond-like carbon (DLC) or the like; an organic insulating materialsuch as epoxy, polyimide, polyamide, polyvinyl phenol, benzocyclobutene,acrylic, or the like; or a siloxane material such as a siloxane resin orthe like. It is to be noted that a siloxane material corresponds to amaterial that contains Si—O—Si bonds. The skeleton structure of siloxaneis formed of bonds of silicon (Si) and oxygen (O). As a substituent, anorganic group that contains at least hydrogen (for example, an alkylgroup or an aromatic hydrocarbon group) is used. As a substituent, afluoro group may be used, as well. In addition, an organic group thatcontains hydrogen at least and a fluoro group may be used. Furthermore,for the insulating layer 2508, after an insulating layer is formed usinga CVD method, a sputtering method, or an ALD method, plasma treatmentmay be performed on the insulating layer in an oxygen atmosphere or anitrogen atmosphere. Here, an example is shown in which the insulatinglayer 2508 has a single-layer structure; however, the insulating layer2508 may be set to have a stacked-layer structure of two or more layers,as well. In addition, the insulating layer 2508 may be formed of anycombination of organic insulating layers and organic insulating layers.For example, the insulating layer 2508 can be formed using materials ofa silicon nitride film or silicon nitride oxide film that can be made tofunction as a passivation layer formed over the entire surface of thesubstrate 2500 and phosphosilicate glass (PSG) or borophosphosilicateglass (BPSG) that can be made to function as a planarization layerformed over the upper layer of the silicon nitride film or siliconnitride oxide film.

The conductive layers 2519 each function as an electrode that functionsas a source electrode or a drain electrode. The conductive layers 2519are electrically connected to the amorphous semiconductor layer 2521,the first single-crystal semiconductor layer 2531, and the secondsingle-crystal semiconductor layer 2541 through the openings formed inthe insulating layer 2508.

For the conductive layers 2519, after a conductive layer is formed as asingle-layer structure or stacked-layer structure over the entiresurface of the substrate using a CVD method or a sputtering method usinga metal element such as aluminum (Al), tungsten (W), titanium (Ti),tantalum (Ta), molybdenum (Mo), nickel (Ni), platinum (Pt), copper (Cu),gold (Au), silver (Ag), manganese (Mn), neodymium (Nd), carbon (C),silicon (Si), or the like or an alloy material or compound material thatcontains any of the metal elements, the conductive layers 2519 can beformed by etching of the conductive layer as selected. For an alloymaterial that contains aluminum, for example, a material that containsaluminum as its main component and nickel and a material that containsaluminum as its main component, nickel, and either one or both of carbonand silicon can be given. Furthermore, for a compound material thatcontains tungsten, for example, a tungsten silicide can be given. Forthe conductive layers 2519, for example, a stacked-layer structure of abarrier layer, an aluminum-silicon (Al—Si) layer, and a barrier layer ora stacked-layer structure of a barrier layer, an aluminum-silicon(Al—Si) layer, a titanium nitride layer, and a barrier layer can beemployed. It is to be noted that a barrier layer corresponds to a thinfilm formed of titanium, a nitride of titanium, molybdenum, or a nitrideof molybdenum. Because aluminum and aluminum silicon have low resistanceand are inexpensive, they are the most suitable for materials used toform the conductive layers that each function as a source electrode ordrain electrode. Moreover, setting the conductive layers that eachfunction as a source electrode or drain electrode to have astacked-layer structure in which barrier layers are provided as a toplayer and a bottom layer is preferable because the formation of hillocksof aluminum or aluminum silicon can be prevented with such a structure.

The terminal electrode 2574 formed in the terminal region 2570 functionsas an electrode used to electrically connect an external input terminalof an FPC or the like to be formed during a subsequent step and thefirst driver circuit section 2530 and second driver circuit section2550. Here, an example is shown in which the terminal electrode 2574 isformed using the same materials of which the conductive layers 2519 areformed.

As described above, the pixel circuit section 2522 in which a transistorthat has the amorphous semiconductor layer 2521 is formed in the displaysection 2520. Furthermore, the peripheral circuit section 2532 in whicha transistor that has the first single-crystal semiconductor layer 2531is formed in the first driver circuit section 2530 and a transistor thathas the second single-crystal semiconductor layer 2541 is formed in thefirst driver circuit section 2530 is formed.

It is to be noted that, in the present embodiment mode, a process inwhich doping and the like are applied to an amorphous semiconductorlayer and a single-crystal semiconductor layer at the same time isdescribed; however, the present invention is not to be taken as beinglimited to use of this kind of structure only. A liquid crystal displaydevice may be fabricated using optimal processes for an amorphoussemiconductor layer and optimal processes for a single-crystalsemiconductor layer. It is to be noted that, in cases in which etching,doping, and the like are applied to an amorphous semiconductor layer anda single-crystal semiconductor layer at the same time, because thefabrication process can be simplified to quite a great extent,significant effects, such as a decrease in costs, an improvement inyield, and the like, can be obtained.

Next, the insulating layer 2509 is formed over the display section 2520and the first driver circuit section 2530. Then, the insulating layer2509 that is formed over the display section 2520 is etched as selected,and an opening that reaches the conductive layer 2519 of the transistorthat is formed in the pixel circuit section 2522 is formed. After theopening is formed in the conductive layer 2519, the pixel electrode 2560is formed so that the opening is buried (with reference to FIG. 27C).

For the insulating layer 2509, formation of a planarization layer bywhich unevenness in the display section 2520 and the first drivercircuit section 2530 can be planarized so that a planar surface isformed is preferable. For example, the planarization layer can be formedusing an organic insulating material such as epoxy, polyimide,polyamide, polyvinyl phenol, benzocyclobutene, acrylic, or the like or asiloxane material such as a siloxane resin or the like. Here, an exampleis shown in which the insulating layer 2509 has a single-layerstructure; however, the insulating layer 2509 may also have astacked-layer structure of two or more layers. When the insulating layer2509 is formed as a stacked-layer structure, for example, the insulatinglayer 2509 can be made to have a stacked-layer structure in which anorganic resin or the like is used in an upper layer and an inorganicinsulating layer of silicon oxide, silicon nitride, silicon oxynitride,or the like is used as a lower layer or a structure in which an organicinsulating layer is interposed between inorganic insulating layers. Theinsulating layer 2509 can be formed as selected using any of-a varietyof different printing methods (screen printing, planographic printing,relief printing, gravure printing, or the like), a liquid dropletdischarge method, a dispenser method, or the like. Alternatively, theinsulating layer 2509 can be formed by an insulating layer first beingformed over the entire surface of the substrate and then etched asselected in regions other than desired regions (here, regions of thedisplay section 2520 and the first driver circuit section 2530).

It is preferable that the pixel electrode 2560 in the present embodimentmode be formed of a material that transmits visible light. For aconductive material that transmits light, indium tin oxide (ITO), indiumtin oxide that contains silicon oxide (ITSO), zinc oxide (ZnO), indiumzinc oxide (IZO), zinc oxide to which gallium has been added (GZO), andthe like can be given. Meanwhile, cases in which the film thickness ofthe pixel electrode 2560 can be made to be thin enough are not limitedto use of the aforementioned materials. This is because, even withmaterials through which light is not transmitted in pixel electrodes ofregular film thickness, light is transmitted in cases in which thethickness of pixel electrodes of such materials is made to be thinenough. In these kinds of cases, a metal element such as tantalum (Ta),tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), chromium(Cr), silver (Ag), or the like or an alloy material or compound materialthat contains any of the metal elements can be used. It is to be notedthat, in cases in which a reflective liquid crystal display device or atransflective liquid crystal display device is fabricated, any of theaforementioned metal elements or the like may be used.

Next, after the spacer 2586 is formed, the alignment film 2582 is formedso as to cover the pixel electrode 2560 and the spacer. Next, thesealant 2580 is formed so as to enclose the display section 2520, thefirst driver circuit section 2530, and the second driver circuit section2550 (with reference to FIG. 28A).

The spacer 2586 can be formed using an organic insulating material suchas epoxy, polyimide, polyamide, polyimide amide, acrylic, or the like oran inorganic insulating material such as silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, or the like as a single-layerstructure or a stacked-layer structure. In the present embodiment mode,in order that a columnar spacer be formed for the spacer 2586, aninsulating layer is formed over the entire surface of the substrate andthen etched and processed so that a spacer with the desired shape isobtained. It is to be noted that there are no particular limitations onthe shape of the spacer 2586, and spherical spacers may be applied, aswell. The width of a cell gap can be retained by use of the spacer 2586.

The alignment film 2582 is a layer by which the liquid crystal can bealigned in a uniform direction. A material may be selected based on theoperation mode of the liquid crystal. For example, the alignment film2582 can be fabricated by formation of a layer using a material ofpolyimide, polyamide, or the like and then performance of alignmenttreatment so that the layer can be made to function as an alignmentfilm. For the alignment treatment, rubbing, irradiation with ultravioletlight rays, or the like may be performed. There are no particularlimitations on the method of formation of the alignment film 2582, andthe alignment film 2582 can be formed over the insulating layer 2509 asselected by use of any of a variety of printing methods or a liquiddroplet discharge method.

The sealant 2580 is formed so as to enclose at least a display region.In the present embodiment mode, a seal pattern is formed so as toenclose the periphery of the display section 2520, the first drivercircuit section 2530, and the second driver circuit section 2550. Forthe sealant 2580, a thermally curable resin or light curable resin canbe used. It is to be noted that the width of the cell gap can beretained by the sealant being made to contain a filler. The sealant 2580is hardened by performance of irradiation with light, thermal treatment,or the like in the sealing of the substrate and another substrate overwhich a counter electrode, a color filter, and the like are providedthat is to be performed in a subsequent step.

The liquid crystal layer 2584 is formed in a region enclosed by thesealant 2580. In addition, the second substrate 2590 over which thecolor filter 2589, the counter electrode 2588, and the alignment film2587 are stacked in the order given is bonded to the first substrate2500 (with reference to FIG. 28B).

The liquid crystal layer 2584 is formed using desired liquid crystalmaterials. Furthermore, the liquid crystal layer 2584 by dripping of aliquid crystal material into a seal pattern that is formed of thesealant 2580. Dripping of the liquid crystal material may be performedusing a dispenser method or a liquid droplet discharge method. It is tobe noted that it is preferable that the liquid crystal material bedegassed under reduced pressure either in advance or after dripping iscompleted. Furthermore, it is preferable that dripping of the liquidcrystal material be performed under an inert gas atmosphere so thatimpurities and the like are not introduced into the liquid crystalmaterial. In addition, it is preferable that steps from after drippingof the liquid crystal material to form the liquid crystal layer 2584 upthrough bonding of the first substrate 2500 and the second substrate2590 be performed at reduced pressure so that air bubbles and the likeare not formed in the liquid crystal layer 2584.

Alternatively, the liquid crystal layer 2584 can be formed by injectionof the liquid crystal material into the frame-shaped pattern that isformed of the sealant 2580 by use of a capillary phenomenon after thefirst substrate 2500 and the second substrate 2590 are bonded together.In this case, a portion that is to be an opening through which theliquid crystal material is injected is formed in advance. It is to benoted that it is preferable that injection of the liquid crystalmaterial be performed at reduced pressure.

After the first substrate 2500 and the second substrate 2590 are made toface each other and brought into close contact with each other, thefirst substrate 2500 and the second substrate 2590 can be attachedtogether by the sealant 2580 being made to harden. At this time, thefirst substrate 2500 and the second substrate 2590 are attached to eachother in such a way that the structure becomes one in which the liquidcrystal layer 2584 is clamped between the alignment film 2587 that isprovided over the second substrate 2590 and the alignment film 2582 thatis provided over the first substrate 2500. It is to be noted that, afterthe first substrate 2500 and the second substrate 2590 are bondedtogether and the liquid crystal layer 2584 is formed, correctingdisarray of the alignment of the liquid crystal layer 2584 byperformance of heat treatment is possible.

For the second substrate 2590, a substrate that can transmit light isused. For example, any of a variety of glass substrates ofaluminosilicate glass, aluminoborosilicate glass, barium borosilicateglass, or the like; a quartz substrate; a ceramic substrate; a sapphiresubstrate; or the like can be used.

Over the second substrate 2590, before bonding is performed, the colorfilter 2589, the counter electrode 2588, and the alignment film 2587 areformed in the order given. It is to be noted that a black matrix may beprovided over the second substrate 2590 in addition to the color filter2589. Furthermore, the color filter 2589 may be provided on the outerside of the second substrate 2590. In addition, when display is set tobe monochrome display, the color filter 2589 need not be provided.Moreover, a sealant may be provided on the second substrate 2590 side,as well. It is to be noted that when a sealant is provided on the secondsubstrate 2590 side, the liquid crystal material is dripped into apattern of the sealant that is provided on the second substrate 2590side.

The counter electrode 2588 can be formed of a conductive material thathas a property by which visible light is transmitted, such as indium tinoxide (ITO), indium tin oxide that contains silicon oxide (ITSO), zincoxide (ZnO), indium zinc oxide (IZO), zinc oxide to which gallium hasbeen added (GZO), or the like. The alignment film 2587 can be formed inthe same way as the alignment film 2582 is formed.

As described above, a structure is obtained in which the display section2520, the first driver circuit section 2530, and the second drivercircuit section 2550 that include the liquid crystal layer 2584 aresealed between the first substrate 2500 and the second substrate 2590.It is to be noted that, in addition to transistors, resistors,capacitors, and the like may be formed in circuit sections provided inthe display section 2520, the first driver circuit section 2530, and thesecond driver circuit section 2550 at the same time. Furthermore, thereare no particular limitations on the structure of any of thetransistors. For example, the structure can be set to be a multi-gatestructure in which a plurality of gates is provided for the amorphoussemiconductor layer or the single-crystal semiconductor layer.

Next, the polarizing plate 2591 and the polarizing plate 2592 areprovided over the first substrate 2500 and the second substrate 2590,and the external input terminal 2578 is connected to the terminalelectrode 2574 via the anisotropic conductive layer 2576 (with referenceto FIG. 28C). Then, a light sensor corresponding to a monitor section ispositioned. It is to be noted that pixels of the monitor section can befabricated in the same way as pixels of the display section. The monitorsection can be formed of one pixel; alternatively, the monitor sectionmay be formed using two or more pixels. The area of the pixel of themonitor section may be the same as the area of the pixel of the displaysection or larger than the area of the pixel of the display section. Bythe monitor section being formed of a plurality of pixels, accuracy inthe detection of luminance can be improved. Furthermore, by the area ofthe pixel of the monitor section being increased, accuracy in detectionof luminance can be improved similarly. In other words, the backlightcan be controlled finely.

The external input terminal 2578 assumes the function of transmission ofsignals (for example, video signals, clock signals, start signals, resetsignals, and the like) and electric potential from external. Here, anFPC is connected as the external input terminal 2578. It is to be notedthat the terminal electrode 2574 is set to be an electrode that iselectrically connected to the first driver circuit section 2530 and thesecond driver circuit section 2550.

By the steps described above, a liquid crystal display device can beobtained. It is to be noted that the present embodiment mode can be usedin combination with any of Embodiment Mode 1 through Embodiment Mode 9,as appropriate.

Embodiment Mode 11

In Embodiment Mode 10, a liquid crystal display device in which asemiconductor substrate of Embodiment Mode 9 is used is described; inthe present embodiment mode, a different kind of display device will bedescribed using FIGS. 29A and 29B.

FIG. 29A is an example of a display device in which a light-emittingelement is used (this kind of display device is also referred to as alight-emitting device or an EL display device). FIG. 29B is an exampleof a display device in which an electrophoretic element is used (thiskind of display device is also referred to as electronic paper or anelectrophoretic display device). Because structures other than those ofdisplay elements are the same as those given in Embodiment Mode 10, adetail description of those structures will be omitted here.

In FIG. 29A, a liquid crystal display device in which a light-emittingelement 2910 is used instead of a liquid crystal element is shown. Here,an example is given in which an organic compound layer 2914 is providedbetween a pixel electrode (cathode) 2912 and a counter electrode (anode)2916. The organic compound layer 2914 has at least a light-emittinglayer and may also have an electron-injecting layer, anelectron-transporting layer, a hole-transporting layer, a hole-injectinglayer, and the like, as well. Furthermore, an end of the pixel electrode(cathode) 2912 is covered with a partition layer 2918. The partitionlayer 2918 may be formed by a film being formed over the entire surfaceof the substrate using an insulating material and then processed so asto expose a portion of the pixel electrode (cathode) 2912, or thepartition layer 2918 may be formed as selected using a liquid dropletdischarge method or the like. The organic compound layer 2914 and thecounter electrode (anode) 2916 are stacked, in the order given, over thepixel electrode (cathode) 2912 and the partition layer 2918. A space2920 between the light-emitting element 2910 and the second substrate2590 may be filled in with an inert gas or the like, or a resin or thelike may be formed in the space 2920.

It is to be noted that, in the present embodiment mode, thelight-emitting element is formed using an organic material; however, thepresent invention is not limited to having this structure only. Thelight-emitting element may also be formed using an organic material, orthe light-emitting element may be formed using a combination of anorganic material and an inorganic material.

In FIG. 29B, a display device in which an electrophoretic element isused instead of a liquid crystal element is shown. Here, an example isgiven in which an electrophoretic layer 2940 is provided between a pixelelectrode 2932 and a counter electrode (a common electrode) 2934. Theelectrophoretic layer 2940 has a plurality of microcapsules 2930 thatare fixed in place by a binder 2936. Each of the microcapsules 2930 hasa diameter of about 10 μm to 200 μm, inclusive, and a transparentliquid, a positively charged white microparticle, and a negativelycharged black microparticle are encapsulated in each microcapsule 2930.If an electric field is applied between the pixel electrode 2932 and thecounter electrode (the common electrode) 2934, the white microparticleand the black microparticle move in opposite directions so that white orblack can be displayed. An electrophoretic element is a display elementin which this principle is applied. By use of an electrophoreticelement, which has a higher reflectance than a liquid crystal element, adisplay portion can be perceived even in a dimly lit place without anykind of an auxiliary light (for example, a front light). In addition,power consumption is low. Moreover, an image which has been displayedonce can be retained even if no power is supplied to the displayportion.

The present invention is essentially geared toward liquid crystaldisplay devices but can be applied to other types of display devices, aswell. For example, luminance control of a light-emitting element in anelectroluminescent display device can be performed instead of control ofoutput of a backlight in a liquid crystal display device. In this case,the structure may be set to be one in which a light sensor is providedso as to be facing a light-emitting element (a light-emitting elementfor monitor use) and changes in luminance of the light-emitting elementare detected. Herewith, display can be performed with a constantluminance being kept even if deterioration of the light-emitting elementgets worse. Furthermore, in a display device in which an electrophoreticelement is used, by performance of correction by reflective light suchthat correct grayscale is displayed, the amount of change in imagequality with change in the environment can be reduced, and excellentimage quality can be displayed. It is to be noted that, in this case,for example, a structure can be employed in which an electrophoreticelement for monitor use, a light source, and a light sensor areprovided; the electrophoretic element for monitor use is irradiated withlight from the light source; and the amount of light reflected from theelectrophoretic element for monitor use is detected using the lightsensor. Here, the light source and the light sensor are arranged so asto be facing the electrophoretic element. Alternatively, the structuremay be one in which no light source is provided and the reflection oflight from external is detected.

The present embodiment mode can be used in combination with any ofEmbodiment Mode 1 through Embodiment Mode 10, as appropriate.

Embodiment Mode 12

Electronic devices in which the liquid crystal display device of thepresent invention is used will be described with reference to FIGS. 30Ato 30H.

For electronic devices in which the liquid crystal display device of thepresent invention is used, cameras such as video cameras, digitalcameras, and the like; goggles-type displays (head-mounted displays);navigation systems; audio playback devices (car audio components and thelike); computers; game machines; portable information terminals (mobilecomputers, cellular phones, portable game machines, electronic bookreaders, and the like); image playback devices provided with storagemedia (specifically, devices that can play storage media such as digitalversatile discs (DVDs) or the like and that are equipped with a displaydevice by which the images can be displayed); and the like can be given.

FIG. 30A is a diagram of a television set or monitor of a personalcomputer. The television set or monitor of a personal computer includesa chassis 3001, a support stand 3002, a display 3003, speakers 3004,video input terminals 3005, and the like. The display device of thepresent invention is used in the display 3003. By the present invention,a television set or monitor of a personal computer with excellent imagequality and high video performance can be provided.

FIG. 30B is a diagram of a digital camera. On the front side part of amain body 3011, an image receiver 3013 is provided, and on the top sidepart of the main body 3011, a shutter button 3016 is provided.Furthermore, on the back side part of the main body 3011, a display3012, operation keys 3014, and an external connection port 3015 areprovided. The display device of the present invention is used in thedisplay 3012. By the present invention, a digital camera with excellentimage quality and high video performance can be provided.

FIG. 30C is a diagram of a notebook computer. In a main body 3021, akeyboard 3024, an external connection port 3025, and a pointing device3026 are provided. Furthermore, a chassis 3022 that has a display 3023is attached to the main body 3021. The display device of the presentinvention is used in the display 3023. By the present invention, anotebook computer with excellent image quality and high videoperformance can be provided.

FIG. 30D is a diagram of a mobile computer that includes a main body3031, a display 3032, a switch 3033, operation keys 3034, an infraredport 3035, and the like. Furthermore, an active matrix display device isprovided in the display 3032. The display device of the presentinvention is used in the display 3032. By the present invention, anotebook computer with excellent image quality and high videoperformance can be provided.

FIG. 30E is a diagram of an image playback device. In a main body 3041,a display 3044, a storage media reader 3045, and operation keys 3046 areprovided. Furthermore, a chassis 3042 that has speakers 3047 and adisplay 3043 is attached to the main body 3041. The liquid crystaldisplay device of the present invention is used in each of the display3043 and the display 3044. By the present invention, an image playbackdevice with excellent image quality and high video performance can beprovided.

FIG. 30F is a diagram of an electronic book reader. In a main body 3051,operation keys 3053 are provided. Furthermore, a plurality of displays3052 is attached to the main body 3051. The display device of thepresent invention is used in each of the displays 3052. By the presentinvention, an electronic book reader with excellent image quality andhigh video performance can be provided.

FIG. 30G is a diagram of a video camera. In a main body 3061, anexternal connection port 3064, a remote control receiver 3065, an imagereceiver 3066, a battery 3067, an audio input 3068, operation keys 3069are provided. Furthermore, a chassis 3063 that has a display 3062 isattached to the main body 3061. The display device of the presentinvention is used in the display 3062. By the present invention, a videocamera with excellent image quality and high video performance can beprovided.

FIG. 30H is a diagram of a cellular phone that includes a main body3071, a chassis 3072, a display 3073, an audio input 3074, an audiooutput 3075, operation keys 3076, an external connection port 3077, anantenna 3078, and the like. The display device of the present inventionis used in the display 3073. By the present invention, a cellular phonewith excellent image quality and high video performance can be provided.

As described above, the range of application of the present invention isextremely wide, and the present invention can be used in electronicdevices of all fields. It is to be noted that the present embodimentmode can be used in combination with Embodiment Mode 1 throughEmbodiment Mode 11, as appropriate.

This application is based on Japanese Patent Application serial no.2007-132607 filed with the Japan Patent Office on May 18, 2007, theentire contents of which are hereby incorporated by reference.

1. A liquid crystal display device comprising: a light source formonitor use; a liquid crystal layer; a backlight for emitting light tothe liquid crystal layer; and a light sensor used to detect an intensityof light passing through the liquid crystal layer from the light sourcefor monitor use.
 2. The liquid crystal display device according to claim1, further comprising: a unit configured to calculate an amount ofcorrection for a luminance of the backlight based on the intensity oflight from the light source for monitor use that is detected by thelight sensor; and a unit configured to control the luminance of thebacklight based on the amount of correction for the luminance of thebacklight that is calculated.
 3. The liquid crystal display deviceaccording to claim 1, further comprising: a unit configured to calculatetiming of the backlight being turned on and timing of the backlightbeing turned off based on the intensity of light from the light sourcefor monitor use that is detected by the light sensor; and a unitconfigured to control the backlight being turned on and the backlightbeing turned off based on the timing of the backlight being turned onand the timing of the backlight being turned off that are calculated. 4.The liquid crystal display device according to claim 1, wherein thelight source for monitor use and the backlight are each provided on oneside of the liquid crystal layer.
 5. The liquid crystal display deviceaccording to claim 1, wherein the light source for monitor use is onepart of the backlight.
 6. The liquid crystal display device according toclaim 1, wherein the light source for monitor use is provided on oneside of the liquid crystal layer and the backlight is provided on a sideof the liquid crystal layer opposite from the side on which the lightsource for monitor use is provided.
 7. The liquid crystal display deviceaccording to claim 1, further comprising a light sensor used to detectan intensity of external light.
 8. An electronic device in which theliquid crystal display device according to claim 1 is used.
 9. A liquidcrystal display device comprising: a liquid crystal layer; a firstpolarizing plate and a second polarizing plate, the liquid crystal layeris sandwiched between the first polarizing plate and the secondpolarizing plate; a light source for monitor use provided on a side ofthe first polarizing plate; a backlight for emitting light to the liquidcrystal layer; and a light sensor provided on a side of the secondpolarizing plate, wherein the light sensor is arranged so as to detectan intensity of light from the light source for monitor use.
 10. Theliquid crystal display device according to claim 9, further comprising:a unit configured to calculate an amount of correction for a luminanceof the backlight based on the intensity of light from the light sourcefor monitor use that is detected by the light sensor; and a unitconfigured to control the luminance of the backlight based on the amountof correction for the luminance of the backlight that is calculated. 11.The liquid crystal display device according to claim 9, furthercomprising: a unit configured to calculate timing of the backlight beingturned on and timing of the backlight being turned off based on theintensity of light from the light source for monitor use that isdetected by the light sensor; and a unit configured to control thebacklight being turned on and the backlight being turned off based onthe timing of the backlight being turned on and the timing of thebacklight being turned off that are calculated.
 12. The liquid crystaldisplay device according to claim 9, wherein the light source formonitor use and the backlight are each provided on one side of theliquid crystal layer.
 13. The liquid crystal display device according toclaim 9, wherein the light source for monitor use is one part of thebacklight.
 14. The liquid crystal display device according to claim 9,wherein the light source for monitor use is provided on one side of theliquid crystal layer and the backlight is provided on a side of theliquid crystal layer opposite from the side on which the light sourcefor monitor use is provided.
 15. The liquid crystal display deviceaccording to claim 9, further comprising a light sensor used to detectan intensity of external light.
 16. An electronic device in which theliquid crystal display device according to claim 9 is used.
 17. Adriving method for a liquid crystal display device comprising: detectingan intensity of light passing through a liquid crystal layer from alight source for monitor use; and controlling a luminance of a backlightbased on the intensity of light from the light source for monitor usethat is detected.
 18. The driving method for a liquid crystal displaydevice according to claim 17, wherein controlling the luminance of thebacklight is performed based on an amount of correction for theluminance of the backlight, and wherein the amount of correction for theluminance of the backlight is calculated based on the intensity of lightfrom the light source for monitor use that is detected.
 19. The drivingmethod for a liquid crystal display device according to claim 17,wherein controlling the luminance of the backlight is performed based onan amount of correction for the luminance of the backlight, and whereinthe amount of correction for the luminance of the backlight iscalculated based on brightness of surroundings detected by a lightsensor that is used to detect the intensity of external light.
 20. Adriving method for a liquid crystal display device comprising: detectingan intensity of light passing through a liquid crystal layer from alight source for monitor use; and controlling a backlight being turnedon and the backlight being turned off based on the intensity of lightfrom the light source for monitor use that is detected.
 21. The drivingmethod for a liquid crystal display device according to claim 20,wherein controlling the backlight being turned on and the backlightbeing turned off is performed based on timing of the backlight beingturned on and timing of the backlight being turned off, and wherein thetiming of the backlight being turned on and the timing of the backlightbeing turned off are calculated based on the intensity of light from thelight source for monitor use that is detected.